JP2007178493A - Cleaning method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cleaning method which allows both side printing with high image quality free of untransfer, and an image forming apparatus using the cleaning method. <P>SOLUTION: The cleaning method which allows both side printing with high image quality free of untransfer is characterized in that cleaning means 25A, 25B to clean first and second image bearing belts 21, 31 are controlled according to image information. The image forming apparatus 100 using the cleaning method is also provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a cleaning method for an image forming apparatus that transfers a toner image formed on a photosensitive member to a transfer material, and transfers the transferred toner image from the transfer material to a recording medium, and an image forming apparatus using the cleaning method. It is.

Conventionally, as a method for recording images on both the front and back sides of a transfer paper, a method is generally used in which the transfer paper once passed through the fixing device is reversed and the toner is transferred to another side of the transfer paper and fixed again. Yes.
However, in this method, the transfer paper is changed in the transport direction, and once the transfer paper is heated and pressurized through the fixing device, the transfer paper is curled. Have.
As a method for solving such a problem, for example, there is one disclosed in Patent Document 1. In this method, after toner images are formed on both sides of the transfer paper, fixing is performed once.
Specifically, the first image formed on the photoconductor is transferred to the transfer belt by the first transfer unit, and then the second image formed on the photoconductor is transferred to one side of the transfer paper by the first transfer unit. Transcript to. Thereafter, the first image on the transfer belt is transferred to the other surface of the transfer paper by the second transfer means, whereby the image is transferred and fixed on both sides of the transfer paper.
However, in the method of Patent Document 1, since the leading edge of the transfer paper is in a free state until the leading edge of the transfer paper having an unfixed image is unloaded from the transfer belt and loaded into the fixing device, it is unfixed. There was a problem that the toner image was disturbed.
Therefore, in Patent Document 2, a toner image is transferred to both sides of a transfer paper, and then the transfer paper is transported to a fixing device. A spur is installed in the transport path to prevent unfixed toner image disturbance. Is disclosed.
However, in this case, the spur that conveys the transfer paper carrying the unfixed toner image to the fixing device becomes soiled with toner over time, and the toner moves to the image, resulting in degradation of image quality. There was a problem that it was.

As a method for solving these problems, Patent Document 3 discloses that a plurality of toner images by a first image forming unit that forms a toner image on a plurality of image carriers having charging, exposing, and developing units around the first intermediate image. A plurality of toner images are second-transferred by a second image forming unit that forms a toner image on a plurality of image carriers having a charging, exposure, and developing unit surrounding them. Pressure transfer and simultaneous fixing, in which the toner image on the first intermediate transfer member and the toner image on the second intermediate transfer member are simultaneously and secondarily transferred onto the front and back surfaces of the transfer material simultaneously. Are disclosed. As a result, an image forming apparatus that performs transfer on both the front and back sides of the transfer material in a batch, assures the accuracy of the image position, and reduces the influence of curling of the transfer material with a single fixing process, thereby increasing print productivity. Could be provided.
However, the pressure transfer fixing method can achieve transfer efficiency close to 100% and does not require cleaning after transfer. However, if toner adheres to unnecessary portions such as between papers, transfer is performed between belts. There was a problem of end. In addition, the transferred toner adheres to the belt and cannot be cleaned, and it adheres to the transfer paper again at the transfer portion, causing a reduction in image. Further, in the non-image portion, in order to determine whether the toner density attached to the second image carrier upper surface is appropriate, the image pattern is placed on the belt and the density is measured. Therefore, there is a problem that the image pattern needs to be cleaned before the second transfer means.

JP-A-1-209470 JP-A-10-142869 JP 2003-43782 A

Accordingly, the present invention has been made in view of the above-described problems, and its object is to provide a cleaning method that enables high-quality double-sided printing without image omission and an image forming apparatus using the cleaning method. That is.

The features of the present invention, which is a means for solving the above problems, are listed below.
The present invention provides a first image carrying unit capable of carrying a first image formed by a first image forming unit on a first image carrying belt, and a second image formed by a second image forming unit. A second image carrying unit that can be carried on a two-image carrying belt, and a transfer for transferring the first image and the second image carried by the first and second image carrying units onto both sides of the recording medium. And a recording medium conveyance path including conveyance means for supplying and conveying the recording medium between the first and second image forming units, and the recording medium conveyance path from the first and second image bearing belts to both sides of the recording medium. In the cleaning method for an image forming apparatus that simultaneously performs pressure transfer, the cleaning method controls a cleaning unit that cleans the first and second image bearing belts according to image information. It is a method.
Further, the present invention is characterized in that the image information is an image range and a non-image range.

The present invention is an image forming apparatus using the cleaning method described above.
The present invention also provides a first image carrying unit capable of carrying the first image formed by the first image forming unit on the first image carrying belt, and a second image formed by the second image forming unit. A second image carrying unit capable of carrying the image on the second image carrying belt, and transferring the first image and the second image carried by the first and second image carrying units to both sides of the recording medium. Transfer means, and a recording medium conveyance path including conveyance means for supplying and conveying the recording medium between the first and second image forming units, and from the first and second image bearing belts to the recording medium. In the image forming apparatus for simultaneously transferring pressure to both sides, a cleaning means for cleaning the first and second image bearing belts is provided between the first transfer means and the second transfer means.

The present invention is characterized in that the cleaning means is blade cleaning.
The present invention is characterized in that the cleaning means is brush cleaning.
The present invention is characterized in that the cleaning means is divided into an image range and a non-image range.
The present invention is characterized in that the surface roughness of the first image bearing belt and the second image bearing belt is (Rz) 10 μm or less.
The present invention is characterized in that a coating layer is provided on the surfaces of the first image carrying belt and the second image carrying belt.

The present invention is characterized in that the average circularity of the toner used is 0.90 to 0.99.
The present invention is characterized in that the toner has a shape factor SF-1 of 120 to 180 and a shape factor SF-2 of 120 to 190.
The present invention is characterized in that the toner used has a Dv / Dn of 1.05-1.30. Here, Dv is a volume average particle diameter (μm), and Dn is a number average particle diameter (μm).

According to the present invention, it is possible to provide a cleaning method that enables high-quality double-sided printing without image omission and an image forming apparatus using the cleaning method.

The best mode for carrying out the present invention will be described below with reference to the drawings. Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. The following description is an example of the best mode of the present invention, and does not limit the scope of the claims.

The present invention provides high image quality without image smearing in the pressure transfer simultaneous fixing method, and a cleaning unit is installed between the first transfer unit and the second transfer unit, and cleaning is controlled according to image information. This solves the problem. In other words, the portion corresponding to the image portion is cleaned by turning OFF (canceling) cleaning and turning ON at the end of image formation (paper interval). Further, the non-image part is divided into the image part and the cleaning means is always operated to perform cleaning.
The present invention can provide a high-quality image forming apparatus free of dirt by controlling cleaning according to image information. In the pressure transfer, if toner adheres in a range where there is no paper (between papers), the toner is fixed on the belt at the transfer portion, and cleaning becomes impossible. Therefore, the cleaning is controlled by the non-image part (between paper) and the image part, and the non-image part (between paper) is cleaned before the transfer, so that there is no problem in the transfer part, and there is no stain and high image quality. An image forming apparatus can be provided.
Further, the cleaning device for cleaning the first and second image bearing belts is provided with a cleaning device between the first transfer device and the second transfer device, so that the toner can be cleaned without being affected by pressure. Can do.
In the present invention, the belt can be cleaned by rubbing the belt surface with the cleaning blade. Further, according to the present invention, the belt can be cleaned by rubbing the belt surface with a brush.
In the present invention, when the surface roughness is set to (Rz) 10 μm or less, the releasability of the toner is increased and the cleaning property is improved. Furthermore, in the present invention, the release property of the toner is improved and the cleaning property is improved by applying a release coating layer of fluororesin such as PFA.

Hereinafter, the configuration and operation of an embodiment according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic central sectional view showing an internal configuration of an image forming apparatus to which the present invention is applied. FIG. 2 is an enlarged view showing the configuration of the first image forming unit. FIG. 3 is an enlarged view showing the configuration of the second image forming unit.
In the image forming apparatus main body 100 shown in FIG. 1, a first image carrier unit 20 having a first image carrier belt 21 that moves endlessly in the direction of the arrow at the upper part with the recording material conveyance path 43A as a boundary, A second image carrier unit 30 having a second image carrier belt 31 that moves endlessly in the direction of the arrow is disposed at the bottom. Four first image forming units 80Y, 80C, 80M, and 80K are provided on the upper tension surface of the first image carrier belt 21, and four first image forming units 80Y, 80C, 80M, and 80K are provided on the inclined tension surface of the second image carrier belt 31. Two image forming units 81Y, 81C, 81M and 81K are provided. Y, C, M, and K along the numbers of the first and second image forming units correspond to the colors of the toner to be handled. Y is yellow, C is cyan, M is magenta, and K is black. Means. Y, C, M, and K are also used in the same meaning with respect to the photoreceptor 1 provided in the first and second image forming units and rotating together with the first image carrying belt 21 and the second image carrying belt 31. . The photoreceptors 1Y to 1K are arranged at the same interval, and at least at the time of image formation, are in contact with a part of the stretched portion between the image bearing belts 21 and 31, respectively.

Although the toner colors to be handled are different, the configurations of the first image forming units 80Y, 80C, 80M, and 80K are the same. The configuration of the first image forming unit 80 will be described with reference to FIG.
In FIG. 2, during operation of the image forming apparatus 100, charging means is provided around a cylindrical photosensitive member 1 that is rotatably supported by a drive source (not shown) so as to rotate in the direction of the arrow according to an electrophotographic process. Image forming members such as the scorotron charger 3, the exposure device 4, the developing device 5, the cleaning device 2, and the light static elimination device Q, the potential sensor S1, and the image sensor S2 are disposed.
The photoreceptor 1 is obtained by forming an organic photosensitive layer (OPC), which is a photoconductive substance, on an aluminum cylinder surface having a diameter of about 30 to 120 mm, for example. A photoconductor on which an amorphous silicon (A-Si) layer is formed can also be used. A belt-like photoreceptor can also be employed. The cleaning device 2 includes a cleaning brush 2a, a cleaning blade 2b, and a recovery member 2c, and removes and recovers foreign matters such as toner remaining on the surface of the photoreceptor.

The exposure device 4 scans the light corresponding to the image data for each color on the surface of each photoreceptor 1 that has been uniformly charged by the charging means, and forms an electrostatic latent image. The exposure apparatus 4 in the illustrated example is an exposure apparatus that includes an LED (light emitting diode) array and an imaging element as light emitting elements, but uses a laser light source, a polygon mirror, etc., and beam light modulated according to image data to be formed. It is also possible to adopt a laser scanning type exposure apparatus.
As the charging means, in addition to the charger 3, a type that is brought into contact with the surface of the photoreceptor 1, for example, a charging roller can be employed.
The development in this embodiment is a development system that employs a two-component developer comprising a toner and a carrier. The electrostatic latent image for each color formed on the surface of each photosensitive member 1 by a laser beam with respect to the negatively charged photosensitive member 1 is developed with toner of a predetermined color having the same polarity (negative polarity) as the charged polarity of the photosensitive member. And become a visible image. So-called reversal development is performed.

The developing device 5 is provided with screws 5c and 5d for stirring and conveying the toner and carrier. When the developing device 5 is mounted on the image forming apparatus 100, one end of the toner replenishing means is connected to a part of the screw 5d. The toner is supplied to the developing roller 5a rotating in the direction of the arrow by the screw 5c, but the thickness of the toner layer on the surface of the developing roller 5a is regulated to a predetermined thickness by the blade 5b. The developing roller 5a is a cylinder made of stainless steel or aluminum, and is supported by the frame of the developing device 5 so as to be rotatable and a distance from the photosensitive member is properly secured, and a predetermined line of magnetic force is formed inside. Has a magnet. The toner used has an average circularity of 0.90 to 0.99, a shape factor SF-1 of 120 to 180, a shape factor SF-2 of 120 to 190, and Dv / Dn of 1.05 to 1.30. is there. Further, a carrier obtained by a conventionally known method is used. The carrier has a volume average particle size of about 25 μm to 60 μm.

The second image forming units 81Y to 81K used in the second image carrier unit 30 will also be described as the second image forming unit 81 with reference to FIG.
The second image forming unit 81 shown in FIG. 3 has the same constituent members as the first image forming unit 80, but the rotational direction of the photoreceptor 1 is different from that of FIG. However, they are mutually shaped with respect to the Y axis passing through the rotation axis 1a of the photosensitive member 1 indicated by an arrow in the drawing.

A first image carrier belt 21 as an image carrier that is supported by a plurality of rollers 24, 25, and 26 (two) and runs in the direction of the arrow is a photoreceptor 1Y, 1C in the first image forming units 80Y to 80K. , 1M, 1K. The image bearing belt 21 is endless, and is stretched and arranged so that a part of each photoconductor after the developing process comes into contact. Further, a primary transfer roller 22 is provided on the inner peripheral portion of the first image carrying belt 21 so as to face each of the photoreceptors 1Y, 1C, 1M, and 1K.
A cleaning device 25 </ b> A is provided on the outer periphery of the first image carrying belt 21. This cleaning device 25A is controlled in accordance with image information, and is divided into an image portion and a non-image portion.
In addition, a density sensor S20 is installed on the outer periphery of the first image carrier belt 21 to determine whether the toner density attached to the upper surface of the first image carrier is appropriate.
The members related to the image carrier belt 21 are integrally configured as the first image carrier unit 20 and can be attached to and detached from the image forming apparatus 100.

A second image carrier belt 31 as an image carrier that is supported by a plurality of rollers 35 and 36 (two pieces) and runs in the direction of the arrow is a photosensitive member 1Y in the second image forming units 81Y to 81K. It is provided in contact with 1C, 1M, and 1K. The image carrying belt 31 is endless and is stretched and arranged so that a part of each photoconductor after the developing process comes into contact. A primary transfer roller 32 is provided on the inner peripheral portion of the image carrying belt 31 so as to face the photoreceptors 1Y, 1C, 1M, and 1K.
A cleaning device 25 </ b> B is provided on the outer peripheral portion of the second image carrying belt 31.
This cleaning device 25B is controlled according to the image information, and is divided into an image portion and a non-image portion.
Further, a density sensor S30 is installed on the outer peripheral portion of the second image carrier belt 31 to determine whether or not the toner density adhering to the second image carrier upper surface is appropriate.
The cleaning devices 25A and 25B employ blades and brushes.
The members related to the image carrier belt 31 are integrally configured as the second image carrier unit 30 and can be attached to and detached from the image forming apparatus 100.

The configuration and material of the image bearing belt will be described. The image bearing belts 21 and 31 are belts having, for example, a resin film having a substrate thickness of 50 to 600 μm as a substrate, and apply a toner image carried by each photoreceptor 1 to the primary transfer rollers 22 and 32. It has a resistance value that enables electrostatic transfer to the belt surface by the bias. As one embodiment, carbon is dispersed in polyimide, and the volume resistance value is adjusted to a resistance of about 10 ⁶ to 10 ¹² Ωcm.
Belt detent ribs for stabilizing the running of the belt are provided on one side or both ends of the belt. The image bearing belts 21 and 31 are provided with a PFA coating layer on the surface in order to obtain toner releasability.

The configuration of the primary transfer roller will be described. As one embodiment, the primary transfer rollers 22 and 32 are obtained by coating the surface of a metal roller serving as a core metal with a conductive rubber material, and a bias is applied to the core metal portion from a power source (not shown). In the conductive rubber material, carbon is dispersed in urethane rubber, and the resistance is adjusted to a volume resistance of about 10 ⁵ Ωcm.

Monochrome recording using only black toner is also possible. In such a case, there are photosensitive members that are not used. Therefore, not only the unused photoreceptors 1Y, 1C, 1M or the developing device 5 are operated, but also a mechanism for keeping these unused photoreceptors and the image carrying belt 21 or 31 in a non-contact state is provided. In this embodiment, an internal frame (not shown) that supports the roller 26 and the primary transfer roller 22 is provided, is supported so as to be rotatable around a certain point, and is rotated in a direction away from the photosensitive member. Thus, only the photosensitive member 1K comes into contact with the image carrier belt 21 or 31, and an image forming process is executed to create a monochrome image using black toner. This is advantageous in terms of improving the life of the photoreceptor.

The secondary transfer device will be described. The secondary transfer device 47 includes transfer rollers 47A and 47B having pressure means, and the secondary transfer rollers 47A and 47B are metal rollers. The images on the first image carrying belt 21 and the second image carrying belt 31 are softened by pressure by pressure, and the image is printed on the paper P while passing a recording medium (hereinafter referred to as paper P) between the secondary transfer rollers 47A and 47B. Transferred and fixed on. The toner softened by the pressure is transferred onto the paper P because the surface of the image bearing belts 21 and 31 is provided with a PFA coating layer so as to obtain the releasability of the toner.

On the right side of the image forming apparatus 100, a paper feeding device 40 that stores paper so as to be fed is provided. Paper feed device (tray) 40a storing a large amount of paper in a plurality of stages, for example, the upper stage, and three stages of paper feed cassettes 40b, 40c, and 40d below each can be pulled out to the right side (operation side) with respect to the paper surface. It is arranged. Among the sheets P stored in the sheet feed tray 40a and the sheet cassettes 40b, 40c, and 40d, the uppermost sheet is selectively fed and separated by the corresponding sheet feeding / separating means 41A to 41D. Only one sheet is reliably sent to the recording medium conveyance paths 43B and 43A by the plurality of conveyance roller pairs 42B.
A pair of registration rollers 45 are provided in the recording medium conveyance path 43A in order to take a feeding timing for feeding the paper P to the secondary transfer position. Further, a jogger 44 for making the position perpendicular to the sheet conveyance direction a normal position is provided in the recording medium conveyance path 43A. The jogger 44 includes guide members that move from both sides toward the edge of the paper in the paper conveyance direction, and the guides press the paper from both sides of the running paper for a moment to align the paper at a predetermined position. .

The sheet P is conveyed from the registration roller pair 45 toward the secondary transfer area.
Note that the recording medium conveyance path 43C having the conveyance roller pair 42C can be supplied with a sheet from another sheet feeding device 300 that can be installed upstream in the conveyance direction. The upper sheet feed surface of the sheet feed tray 40a is arranged so that the uppermost sheet in the sheet feed tray 40a is fed and then conveyed substantially horizontally without being bent. Therefore, even thick paper and highly rigid paperboard can be reliably fed. In addition, it is convenient to adopt an air paper feed made up of a vacuum mechanism so that the paper feed tray 40a can reliably feed papers having various characteristics. Although not shown, a sensor for detecting a sheet is provided at a key point of the recording material conveyance path, and serves as a trigger for various signals based on the presence of the sheet.
In the secondary transfer device 47, in order to make the color and glossiness of the images on both sides of the paper the same, the material of the roller and belt, the hardness, etc. are made equal in the up and down direction.
The paper discharge roller pair 71 discharges and stacks the paper on a paper discharge stack unit 75 provided on the left side of the image forming apparatus 100.
The operation provided on the upper surface of the image forming apparatus 100, the display unit 90 is provided with a keyboard or the like, and conditions for image formation can be input, the state of the apparatus is displayed on the display unit, and the operator and Information exchange with the image forming apparatus is facilitated. Further, in the electrical / control device 95 provided in the image forming apparatus 100, various power supplies, control boards, and the like are protected and housed in a sheet metal frame. Reference numeral 200 denotes a document reading device, and 300 denotes a paper feeding device that can be additionally installed.

Next, an operation during single-sided recording in which a full-color image is formed on one side of the paper P in the above configuration will be described.
There are basically two types of single-sided recording methods that can be selected. One of the two types is a method of directly transferring an image carried on the first image carrying belt 21 to one side of the paper, and the other method is an image carried on the second image carrying belt 31. Is directly transferred onto one side of the paper. In the present embodiment, because of the configuration of the image forming apparatus 100, when an image carried on the first image carrying belt 21 is directly transferred to one side of the paper, the image is placed on the upper surface of the paper and the second image carrying belt. When the image carried on 31 is directly transferred to one side of the paper, the image is formed on the lower surface of the paper. In the case where the data to be recorded is a plurality of pages, it is convenient to control the image forming order so that the pages are aligned on the paper discharge stack unit 75.

An explanation will be given of a method in which an image is carried on the first image carrying belt 21 and then transferred to a sheet so that the pages are arranged in order from the image data of the last page. When the image forming apparatus 100 is operated, the photoreceptors 1Y, 1C, 1M, and 1K in the first image carrying belt 21 and the first image forming units 80Y to 80K rotate. At the same time, the second image carrier belt 31 rotates. However, the photoreceptors 1Y, 1C, 1M, and 1K in the second image forming units 81Y to 81K are separated from the second image carrier belt 31 and are not rotated. Is done. First, image formation by the image forming unit 80Y is started. By the operation of the exposure device 4 composed of an LED (light emitting diode) array and an imaging element, light corresponding to image data for yellow emitted from the LED is irradiated onto the surface of the photoreceptor 1Y uniformly charged by the charging device 3. Thus, an electrostatic latent image is formed.
This electrostatic latent image is developed with yellow toner by the developing roller 5a, becomes a visible image, and is electrostatically applied on the first image carrying belt 21 that moves in synchronization with the photoreceptor 1Y by the transfer action of the primary transfer roller 22. Primary transfer. Such latent image formation, development, and primary transfer operations are sequentially performed in the same manner on the photosensitive members 1C, 1M, and 1K.
As a result, yellow, cyan, magenta, and black toner images are carried on the first image carrying belt 21 as sequentially overlapping full-color toner images, and are moved in the direction of the arrow together with the first image carrying belt 21. .

At the same time, the paper P used for recording is fed out from the paper feed tray 40a or the paper feed cassettes 40b to 40d in the paper feed device 40 by one of the paper feed / separation means 41A to 41D for feeding the paper P. The pair 42B and 42C are conveyed to the recording material conveyance path 43C. Before the leading edge of the paper is picked up by the registration roller pair 45, the jogger 44 operates to push both sides of the paper from both lateral directions with respect to the paper conveyance direction, and the lateral alignment of the paper is not performed. I can be taken. The registration roller pair 45 is stationary, and the leading edge of the sheet is stationary while entering the nip of the registration roller pair 45, but the timing is set so that the position with the image on the first image carrier belt 21 is normal. Then, the registration roller pair 45 is rotated to convey the sheet to the transfer area.
FIG. 4 is a diagram illustrating a cleaning operation of the cleaning device. The cleaning device 25 </ b> A performs cleaning on the first image carrier belt 21 at a timing. When the image unit is retracted by the cleaning device and the passage of the image unit is completed, the cleaning device comes into contact with the belt and cleans the gap between the sheets. When the next image comes, the cleaning device retreats from the belt. The contact with the belt for cleaning is performed by a solenoid (not shown).
FIG. 5 is a diagram showing the relationship between the cleaning operation and the density detection by the sensor. In order to detect an abnormality in the primary transfer process, an image pattern is attached to the surface of the non-image portion belt, and a sensor detects whether the toner density is appropriate. Therefore, when the adhesion passes through the transfer portion, the sheet is not a non-image portion and does not exist, so that the toner is softened and fixed by pressure. Therefore, it is necessary to perform cleaning before transfer.
In the present invention, the image portion is controlled to be cleaned according to the image information, and the non-image portion is always cleaned. Further, according to the present invention, the image portion can be controlled according to the image information by dividing the cleaning into the image portion and the non-image portion.

The full-color toner image on the first image carrying belt 21 is transferred to the upper surface of the sheet P conveyed in synchronization with the first image carrying belt 21 under the pressure action of the secondary transfer rollers 47A and 47B.
Further, foreign matters such as toner remaining on the surfaces of the photoreceptors 1Y, 1C, 1M, and 1K in the first image forming units 80Y to 80K that have finished the primary transfer are removed by the cleaning brush 2a and the cleaning blade 2b of the cleaning device 2. It is removed from the surface of each photoconductor. The surface of each photoconductor is neutralized by a residual potential by the static eliminator Q to prepare for the next image formation / transfer process. Sensors S1 and S2 detect whether the surface potential after exposure on the surface of the photoconductor and the concentration of toner attached to the surface of the photoconductor after the development process are appropriate, and appropriately set image forming conditions. Information is sent to a control means (not shown) for control.

The toner of each color on the first image carrying belt 21 is subjected to the pressure action of the transfer device 47, and the toner is softened, melted and mixed, and is completely transferred as a color image on the paper P due to the releasability of the belt.
Thereafter, the paper is discharged by the paper discharge roller 71 onto the paper discharge stack 75 with the image surface facing upward. In the paper discharge stack section 75, the image forming order is programmed so that the recorded matter of the young pages is stacked so as to be sequentially stacked on top, so the page order is aligned. Since the paper discharge stack unit 75 is lowered as the number of discharged paper sheets increases, the paper sheets can be stacked in an orderly and reliable manner, and the page order is not disturbed. Instead of stacking the recorded paper directly on the paper discharge stack section 75, it is possible to carry out a punching process or to transport it to a post-processing device such as a sorter, a collator, a binding device or a folding device.
In another method of forming an image on one side of the paper P, image formation is performed in order from the image data of young pages in order not to form an image in the first image forming units 80Y to 80K and for page alignment. However, it is basically the same as the one-side recording process described above.

Next, the operation during double-sided recording in which images are formed on both sides of the paper P will be described. When a start signal is input to the image forming apparatus, the first image carrying belt 21 displays an image for each color sequentially formed by the first image forming units 80Y, 80C, 80M, and 80K described in the single-sided recording operation. The image for each color sequentially formed by the second image forming units 81Y, 81C, 81M, 81K is applied to the second image carrier belt 31 substantially in parallel with the step of carrying out the primary transfer sequentially and carrying it as the first image. A step of sequentially performing primary transfer and carrying as a second image is performed. With the configuration shown in FIG. 1, in order for the first image and the second image to coincide with each other at the leading edge in the sheet transport direction, the second image is formed after the start of the first image formation. Is started. Further, since the sheet is stopped and retransmitted by the registration roller pair 45, the sheet is fed in consideration of the time and is aligned by the jogger 44. The registration roller pair 45 conveys the sheet to a transfer nip as a secondary transfer unit at a timing.
The cleaning device performs the same operation on the second image bearing belt as the cleaning of the first image bearing belt on one side. The cleaning devices 25A and 25B perform cleaning on the first image carrier belt 21 and the second image carrier belt 31 in a timely manner. When the image unit is retracted by the cleaning device and the passage of the image unit is completed, the cleaning device comes into contact with the belt and cleans the gap between the sheets. When the next image comes, the cleaning device retreats from the belt. The contact with the belt for cleaning is performed by a solenoid (not shown) (see FIG. 4).
Further, in order to detect an abnormality in the primary transfer process also in the second image bearing belt 31, an image pattern is attached to the surface of the non-image portion belt, and a sensor is used to detect whether the toner density is appropriate. Yes. Therefore, when the adhesion passes through the transfer portion, the toner does not exist because the sheet is not a non-image portion, so that the toner is softened and fixed by pressure. Therefore, it is necessary to perform cleaning before transfer (see FIG. 5). .

The toners of the respective colors on the first image carrying belt 21 and the second image carrying belt 31 are melted and mixed by the transfer roller 47A and B by the pressure action of the transfer device 47, and the toner is released onto the paper P due to the releasability of the belt. Fully color image is transferred on both sides simultaneously. In this way, the paper P having the full color toner image transferred on both sides is discharged. The paper P is discharged onto the paper discharge stack unit 75 by the paper discharge roller 71.
When double-sided recording is performed on a plurality of pages of paper, the image formation order is controlled so that the image of a young page becomes the bottom surface and is stacked on the paper discharge stack unit 75. The order of the pages is 1 page in order from the top, 2 pages on the back, 3 pages on the second sheet, and 4 pages on the back. Such image formation order control and cleaning control are executed by a control means (not shown).
As for the single-sided recording and the double-sided recording operation, an example in which full-color recording is executed has been described, but monochrome recording using only black toner is also possible.

The circularity and circularity distribution will be described.
It is important that the toner in the present invention has a specific shape and shape distribution. An toner having an average circularity of less than 0.90 and an irregular shape that is too far from a spherical shape exhibits satisfactory transferability and dust. A high-quality image with no image cannot be obtained. As a method for measuring the shape, an optical detection band method is suitable in which a suspension containing particles is passed through an imaging unit detection band on a flat plate, and a particle image is optically detected and analyzed by a CCD camera. Toner having an average circularity of 0.90 to 0.99, which is a value obtained by dividing the perimeter of an equivalent circle having the same projected area obtained by this method by the perimeter of the actual particle, has high reproducibility with an appropriate density reproducibility. It was effective in forming a clear image. More preferably, particles having an average circularity of 0.93 to 0.97 and a circularity of less than 0.94 are 10% or less.
When the average circularity exceeds 0.99, in a system that employs blade cleaning or the like, poor cleaning occurs on the photosensitive member and the transfer belt, causing stains on the image. For example, when outputting an image with a low image area ratio, there is little transfer residual toner and there is no problem with poor cleaning. However, when outputting an image with a high image area ratio such as a color photographic image, If an untransferred image remains on the photoreceptor due to a defect or the like, a cleaning defect is likely to occur. If the above-mentioned cleaning failures occur frequently, further, the charging roller that contacts and charges the photoreceptor is contaminated, and the original charging ability cannot be exhibited.

A method for measuring the circularity will be described.
The average circularity can be measured by a flow type particle image analyzer FPIA-2100 (manufactured by Toa Medical Electronics Co., Ltd.). As a specific measurement method, 0.1 to 0.5 mL of a surfactant, preferably alkylbenzene sulfonate is added as a dispersant in 100 to 150 mL of water from which impure solids have been removed in advance, and further measurement is performed. Add about 0.1-0.5g of sample. The suspension in which the sample is dispersed is obtained by performing a dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes and measuring the shape and distribution of the toner with the above apparatus at a dispersion concentration of 3000 to 10,000 / μL. .

The shape factors SF-1 and SF-2 will be described.
As shown in FIG. 6, the shape factor SF-1 here is a value indicating the ratio of the roundness of the shape of the spherical substance, and is the maximum of the elliptical figure formed by projecting the spherical substance on a two-dimensional plane. It is represented by a value obtained by dividing the square of the length MXLNG by the graphic area AREA and multiplying by 100π / 4.
That is, the shape factor SF-1 is expressed by the following equation:
SF-1 = {(MXLNG) ² / AREA} × (100π / 4)
Is defined by
When the value of SF-1 is 100, the shape of the substance becomes a true sphere, and as the value of SF-1 increases, the shape of the substance becomes indefinite.
Further, as shown in FIG. 7, the shape factor SF-2 is a numerical value indicating the ratio of the unevenness of the shape of the substance, and the square of the perimeter PERI of the figure formed by projecting the substance on the two-dimensional plane is the figure area. It is expressed as a value when divided by AREA and multiplied by 100 / 4π.
That is, the shape factor SF-2 is expressed by the following equation:
SF-2 = {(PERI) ² / AREA} × (100 / 4π).
When the value of SF-2 is 100, there is no unevenness on the surface of the substance, and as the value of SF-2 increases, the unevenness on the surface of the substance becomes more prominent.
In the embodiment of the present invention, a toner image is randomly sampled 100 times using an FE-SEM (S-800) manufactured by Hitachi, and the image information is stored in an image analysis apparatus (LUSEX3) manufactured by Nireco. Introduced and analyzed, calculated from the above formula.
It has been clarified by the present inventors that the transfer efficiency increases when the toner shape approaches the spherical shape as much as possible (both SF-1 and SF-2 approach 100). This is because there is only point contact between the toner particles and those that come into contact with the toner particles due to the shape effect (toner particles, image carrier, etc.), so that the toner fluidity is increased or the toner is adsorbed to the image carrier, etc. This is thought to be because the force is weakened and it is easily affected by the transfer electric field.
On the other hand, when the shape of the toner approaches a spherical shape, it is disadvantageous for mechanical cleaning such as blade cleaning. As described above, this increases the toner fluidity or weakens the adsorbing force on the image carrier and the toner easily passes through a slight gap between the cleaning member and the image carrier. Therefore, from the viewpoint of cleaning properties, the shape of the toner is somewhat irregular (in the direction in which the value of SF-1 is greater than 100) or uneven (in the direction in which the value of SF-2 is greater than 100). It is more preferable.

Dv / Dn (ratio of volume average particle diameter / number average particle diameter) will be described.
The toner has a volume average particle diameter (Dv) of 4 to 8 μm and a ratio (Dv / Dn) to the number average particle diameter (Dn) of 1.05 to 1.30, preferably 1.10 to 1.25. According to the dry toner, the particle size distribution of the toner becomes narrow, so that the following merits occur.
(1) Since a phenomenon in which toner particles having a toner particle size corresponding to an image pattern, which is selective development on the toner particle size surface, is less likely to occur, a stable image is always formed. Can do.
(2) When the toner recycling system is mounted, a large amount of small-size toner particles that are difficult to transfer are recycled in quantity. However, since the toner particle size distribution is originally narrow, it is difficult to receive the above-described action. Therefore, a stable image can always be formed.
(3) In the two-component developer, even if the toner balance for a long time is performed, the fluctuation of the toner particle diameter in the developer is reduced, and a good and stable developability is obtained even in the long-term stirring in the developing device. can get.
(4) Even when used as a one-component developer, even if the balance of the toner is performed, the fluctuation of the toner particle diameter is reduced, the filming of the toner on the developing roller, and the toner is thinned. Therefore, the toner was not fused to a member such as a blade, and good and stable developability and images were obtained even when the developing device was used and stirred for a long time.
In general, it is said that the smaller the toner particle size, the more advantageous it is to obtain a high-resolution and high-quality image, but it is disadvantageous for transferability and cleaning properties. is there. Further, when the volume average particle diameter is smaller than the range of the present invention, in the case of a two-component developer, the toner is fused to the surface of the carrier during a long period of stirring in the developing device, and the charging ability of the carrier is lowered, When used as an agent, toner filming on the developing roller and toner fusion to a member such as a blade for thinning the toner are likely to occur. Further, these phenomena are the same for the toner having a fine powder content larger than the range of the present invention.
On the contrary, when the particle diameter of the toner is larger than the range of the present invention, it becomes difficult to obtain a high resolution and high quality image, and when the balance of the toner in the developer is performed, In many cases, the variation of the particle size becomes large. It was also clarified that the same applies when the volume average particle diameter / number average particle diameter is larger than 1.30.
Further, when the volume average particle diameter / number average particle diameter is smaller than 1.05, there is a preferable aspect from the viewpoint of stabilizing the behavior of the toner and uniforming the charge amount, but the thin line portion is developed with small size particles. On the other hand, it is difficult to separate the functions depending on the toner particle diameter, such as developing a solid image mainly on large-size particles, which is not preferable.

A method for measuring the toner particle size will be described.
Examples of the measuring device for the particle size distribution of toner particles by the Coulter counter method include Coulter Counter TA-II and Coulter Multisizer II (both manufactured by Coulter). The measurement method is described below.
First, 0.1 to 5 mL of a surfactant (preferably alkylbenzene sulfonate) is added as a dispersant to 100 to 150 mL of the electrolytic aqueous solution. Here, the electrolytic solution is a solution prepared by preparing a 1% NaCl aqueous solution using primary sodium chloride. For example, ISOTON-II (manufactured by Coulter) can be used. Here, 2 to 20 mg of a measurement sample is further added. The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes, and the measuring device is used to measure the volume and number of toner particles or toner using a 100 μm aperture as an aperture. Volume distribution and number distribution are calculated. From the obtained distribution, the volume average particle diameter (Dv) and the number average particle diameter (Dn) of the toner can be obtained.
As channels, 2.00 to less than 2.52 μm; 2.52 to less than 3.17 μm; 3.17 to less than 4.00 μm; 4.00 to less than 5.04 μm; 5.04 to less than 6.35 μm; 6 .35 to less than 8.00 μm; 8.00 to less than 10.08 μm; 10.08 to less than 12.70 μm; 12.70 to less than 16.00 μm; 16.00 to less than 20.20 μm; Uses 13 channels of less than 40 μm; 25.40 to less than 32.00 μm; 32.00 to less than 40.30 μm, and targets particles having a particle size of 2.00 μm to less than 40.30 μm.

1 is a schematic central sectional view showing an internal configuration of an image forming apparatus to which the present invention is applied. FIG. 3 is an enlarged view showing a configuration of a first image forming unit. FIG. 4 is an enlarged view showing a configuration of a second image forming unit. It is a figure showing cleaning operation of a cleaning device. It is the figure which showed the relationship between cleaning operation | movement and the density | concentration detection by a sensor. FIG. 4 is a diagram schematically illustrating the shape of a toner for explaining a shape factor SF-1. FIG. 6 is a diagram schematically illustrating the shape of a toner for explaining a shape factor SF-2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Cleaning apparatus 2a Cleaning blade 2b Cleaning brush 2c Waste toner collection | recovery means 3 Charging means (Scorotron charger)
4 exposure device 5 developing device 5a developing roller 5b regulating blade 5c, 5d stirring means 5e toner sensor 20 first image carrier unit 21 first image carrier belt 22 primary transfer rollers 23 to 29 first image carrier belt support roller 24 Driving roller 25A, 25B cleaning means 26 Image-receiving surface maintaining roller (two)
30 Second image carrier unit 31 Second image carrier belt
32 Primary transfer roller 35 for second image carrier unit 35 Driving roller 36 Image-receiving surface maintaining roller (2 pieces)
40 Paper feeder
40a Upper paper feeder (tray)
40b to 40d Paper feed cassettes 41A to 41D Paper feed / separation means 42A to 42C Transport roller pairs 43A to 43C Recording material transport path 44 Jogger
45 Registration roller pair 47 Secondary transfer means 47A Transfer roller 47B Transfer roller 71 Discharge roller pair 75 Discharge stack unit 80 First image forming unit 81 Second image forming unit 90 Operation / display unit (unit)
95 Electrical Equipment / Control Device 100 Image Forming Device 200 Document Reading Device 300 Additional Sheet Feeder A1, A2 Arrow Y Yellow C Cyan M Magenta K Black Q Static Eliminator Y Axis Vertical Coordinate Axis H Drive Axis S20, S30 Toner sensor

Claims (12)

A first image carrying unit capable of carrying a first image formed by the first image forming unit on a first image carrying belt;
A second image carrying unit capable of carrying a second image formed by the second image forming unit on a second image carrying belt;
Transfer means for transferring the first image and the second image carried by the first and second image carrying units to both surfaces of the recording medium;
A recording medium conveyance path including conveyance means for supplying and conveying the recording medium between the first and second image forming units,
In the method of cleaning an image forming apparatus in which pressure is simultaneously transferred from the first and second image bearing belts to both sides of the recording medium,
In the cleaning method, a cleaning unit that cleans the first and second image bearing belts is controlled according to image information. The cleaning method according to claim 1,
In the cleaning method, the image information is an image range and a non-image range. An image forming apparatus using the cleaning method according to claim 1. A first image carrying unit capable of carrying a first image formed by the first image forming unit on a first image carrying belt;
A second image carrying unit capable of carrying a second image formed by the second image forming unit on a second image carrying belt;
Transfer means for transferring the first image and the second image carried by the first and second image carrying units to both surfaces of the recording medium;
A recording medium conveyance path including conveyance means for supplying and conveying the recording medium between the first and second image forming units,
In the image forming apparatus for simultaneously transferring pressure from the first and second image bearing belts to both sides of the recording medium,
An image forming apparatus, wherein a cleaning unit for cleaning the first and second image bearing belts is provided between the first transfer unit and the second transfer unit. The image forming apparatus according to claim 3 or 4,
In the image forming apparatus, the cleaning unit is blade cleaning. The image forming apparatus according to claim 3 or 4,
In the image forming apparatus, the cleaning unit is brush cleaning. The image forming apparatus according to claim 3 or 4,
In the image forming apparatus, the cleaning unit is divided into an image range and a non-image range. The image forming apparatus according to claim 3 or 4,
In the image forming apparatus, the surface roughness of the first image bearing belt and the second image bearing belt is (Rz) 10 μm or less. The image forming apparatus according to claim 3 or 4,
In the image forming apparatus, a coating layer is provided on the surfaces of the first image bearing belt and the second image bearing belt. The image forming apparatus according to claim 3 or 4,
In the image forming apparatus, the average circularity of toner used is 0.90 to 0.99. The image forming apparatus according to claim 3 or 4,
In the image forming apparatus, the toner has a shape factor SF-1 of 120 to 180,
An image forming apparatus having a shape factor SF-2 of 120 to 190. The image forming apparatus according to claim 3 or 4,
In the image forming apparatus, Dv / Dn of toner used is 1.05-1.30.

Images