JP2006184644A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the defective transfer of a 1st toner image at a prestage transfer part, regarding a one pass system copier for transferring a 1st toner image on a 1st intermediate transfer belt 21 to the 1st surface of a transfer sheet P at the prestage transfer part, thereafter, transferring a 2nd toner image on a 2nd intermediate transfer belt 31 to the 2nd surface of the transfer sheet at a poststage transfer part. <P>SOLUTION: The 2nd intermediate transfer belt 31 is arranged at a position away from the prestage transfer part, and also, a transfer roller 46 as a conductive member coming in contact with the 1st intermediate transfer belt 31 is arranged in the prestage transfer part, and the transfer sheet P is inserted in between the 1st intermediate transfer belt 21 and the transfer roller 46 in the prestage transfer part, then, the transfer sheet P is pressurized by the transfer roller 46 from the 2nd surface side toward the 1st intermediate transfer belt 21, then, the 1st toner image on the 1st intermediate transfer belt 21 is transferred to the 1st surface. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile, or a printer that forms images on both sides of a recording medium such as transfer paper by a so-called one-pass method.

  2. Description of the Related Art Conventionally, as an image forming apparatus that forms an image on both sides of a recording medium, an apparatus using a switchback method described in Patent Document 1 is known. In the switchback method, the recording medium is passed through a transfer unit and a fixing unit, an image is recorded on one surface of the recording unit, and then the recording unit is reversed by a reverse conveyance path. Then, the image is recorded on the other side by switching back to the transfer unit and the fixing unit.

  Also known is an image forming apparatus described in Patent Documents 2, 3, 4, 5, etc. that forms images on both sides of a recording medium by a one-pass method. In these image forming apparatuses, first, the second toner image carrier is moved from the photosensitive member or the first intermediate transfer belt toward the intermediate transfer belt or the second intermediate transfer belt as the second toner image carrier. Transfer the toner image. Next, a transfer sheet as a recording medium is sandwiched in a pre-stage transfer portion which is a contact portion between the first toner image carrier and the second toner image carrier, and the first surface of the transfer paper is placed on the first toner image carrier. And the second surface is in close contact with the second toner image carrier. A transfer current is passed between the first toner image carrier and the second toner image carrier to electrostatically transfer the first toner image on the first toner image carrier to the first surface of the transfer paper. Next, after the transfer paper is discharged from the preceding transfer section, the second transfer section in which the second toner image carrier and the transfer charger face each other with a predetermined gap due to the surface movement of the second toner image carrier. Transport to. Then, in this latter transfer section, an electric charge is applied to the first surface of the transfer paper, and the second toner image is transferred from the second toner image carrier in contact with the second surface to the second surface. That is, in the image forming apparatuses described in Patent Documents 2, 3, 4, and 5, after the first toner image is electrostatically transferred to the first surface of the transfer paper by the contact method in the front transfer unit, the second transfer unit in the second transfer unit. The toner image is transferred to the second surface of the transfer paper by a non-contact charger method. By such toner image transfer, a one-pass method is realized in which toner images are formed on both sides of a recording medium that has been passed through the transfer device only once. In the one-pass method, it is not necessary to switch back the recording medium and pass through the transfer device twice, so that the image forming speed can be increased as compared with the switch-back method.

JP-A-5-8948 JP 2000-187401 A JP 2002-244455 A JP 2002-202638 A JP 2004-109493 A

  While the present inventor has studied an image forming apparatus that forms an image on both sides of a recording medium in this way by a one-pass method, the transfer is performed when the first toner image is transferred to the first side of the recording body. We found that it may cause defects. It has also been found that such a transfer failure occurs when the density difference of the second toner image becomes relatively large or when the image portion of the second toner image becomes relatively scattered.

  Therefore, the present inventor conducted intensive studies on the cause of such transfer defects, and has found the following. That is, when the density difference of the second toner image becomes relatively large or the image portion of the second toner image becomes relatively scattered, the transfer current value in the above-mentioned transfer direction in the front transfer portion is changed. It has been found that variations tend to occur.

  FIG. 1 is an enlarged schematic diagram illustrating an example of the configuration of the front transfer unit. In the figure, reference numeral 21 denotes a first intermediate transfer belt as a first toner image carrier that carries a first toner image recorded on the first surface of the recording body. Reference numeral 31 denotes a second intermediate transfer belt as a second toner image carrier that carries the second toner image recorded on the second surface of the recording body. In the series of image forming processes, when the transfer process is not performed, the first intermediate transfer belt 21 and the second intermediate transfer belt 31 in FIG. When the transfer process is started, the transfer paper P as a recording medium is fed into the contact portion of both intermediate transfer belts and is sandwiched between both intermediate transfer belts as shown in FIG. The first surface of the transfer paper P is in close contact with the first intermediate transfer belt 21 and the second surface is in close contact with the second intermediate transfer belt 31.

  In the front transfer portion, a transfer roller 46, which is a conductive member, is in contact with the back surface of the second intermediate transfer belt 31, and a transfer bias having a polarity opposite to the charging polarity of the toner (plus in the illustrated example) is present. Applied. A transfer counter roller 28 is in contact with the back surface of the first intermediate transfer belt 21 and is grounded. With this configuration, a transfer current flows between the transfer counter roller 28 and the transfer roller 46 through the first intermediate transfer belt 21, the transfer paper P, and the second intermediate transfer belt 31 in the upstream transfer unit.

  FIG. 2 is an enlarged schematic diagram showing the pre-transfer portion when a solid second toner image is formed without the image portions being scattered. As shown in the figure, when a solid second toner image p2 having a uniform thickness in the paper surface direction is formed, the value of the transfer current becomes substantially uniform in the paper surface direction. In such a case, transfer failure of the second toner image p2 is unlikely to occur in the front transfer portion.

  FIG. 3 is an enlarged schematic diagram showing the pre-transfer portion when the second toner image p2 in which the image portions are scattered is formed. As shown in the drawing, when the image portions of the second toner image are scattered, the transfer current flowing through the non-image portion is larger than the transfer current flowing through the image portion. The value of the transfer current varies greatly in the direction of the paper. When the value of the transfer current varies in this way, the transfer current in the image portion becomes insufficient, and transfer defects are likely to occur. For this reason, transfer defects have occurred. In addition, the transfer failure in the case where the second toner image p2 is formed in a state where the image portions are scattered is described. However, the case where the image in which the difference in density of the image portions is relatively large is also formed. The same transfer failure is likely to occur. This is because the thickness of the toner layer at the high density portion becomes larger than the thickness of the toner layer at the low concentration portion, and the transfer current flowing through the high density portion becomes smaller than the transfer current flowing through the low density portion.

  The present invention has been made in view of the above background, and an object of the present invention is to provide a one-pass image forming apparatus capable of suppressing the transfer failure of the first toner image in the preceding transfer unit. .

In order to achieve the above object, according to the first aspect of the present invention, the first toner image recorded on the first surface of the recording body is formed on the first toner image carrier, and the recording is performed on the second surface of the recording body. Toner image forming means for forming the second toner image to be formed on the second toner image carrier, and the first toner image carrier at the pre-transfer portion that brings the first toner image carrier and the first surface into contact with each other. A transfer current is generated between the body and the first surface to transfer the first toner image to the first surface, and then the charge applying means is opposed to the first surface through a predetermined gap. In the subsequent transfer section, the second toner image is applied to the first surface by the charge applying means while contacting the second toner image carrier and the second surface, and the second toner image is transferred to the second surface. Transfer means for transferring to the surface, and fixing means for fixing the toner images on both sides of the recording medium after passing through the transfer means. In the image forming apparatus for forming images on both sides of the recording medium by the one-pass method, the second toner image carrier is disposed at a position away from the front transfer portion, and the first toner image carrier is disposed on the first toner image carrier. An abutting conductive member is provided in the preceding transfer portion, and the recording member is sandwiched between the first toner image carrier and the conductive member at the preceding transfer portion, and the recording member is used to record the recording member. The transfer means is configured to transfer the first toner image on the first toner image carrier to the first surface while pressing the body from the second surface side toward the first toner image carrier. It is characterized by comprising.
According to a second aspect of the present invention, the first toner image recorded on the first surface of the recording medium and the second toner image recorded on the second surface of the recording medium are made the same toner based on the image information. Toner image forming means for forming on an image carrier or forming individual toner images on different toner image carriers, the surface of the toner image carrier on which the first toner image is formed, and the first surface At a pre-transfer portion that causes the toner image carrier to contact with the first surface, a transfer current is generated between the surface of the toner image carrier and the first surface, and the first toner image is transferred from the surface of the toner image carrier to the first surface. After the transfer, the second toner image carrier and the second surface are brought into contact with each other at the subsequent transfer portion where the charge applying means is opposed to the first surface through a predetermined gap. Means for applying a charge to the first surface and transferring the second toner image to the second surface. And an image forming apparatus for forming an image on both sides of the recording medium by a one-pass method, and fixing means for fixing the toner images on both sides of the recording medium after passing through the transfer means. Accordingly, the relationship between the first toner image and the second toner image is reversed to form the first toner image as the second toner image and the second toner image as the first toner image. The toner image forming means is configured as described above.
According to a third aspect of the present invention, in the image forming apparatus of the second aspect, the maximum image density and the minimum image density of the toner image included in the image information or calculated based on the image information. In accordance with the difference, the toner image forming means is configured to form the respective toner images by reversing the relationship between the first toner image and the second toner image.
According to a fourth aspect of the present invention, in the image forming apparatus according to the second aspect, the image area ratio information of the toner image that is included in the image information or calculated based on the image information is used. The toner image forming means is configured to form the respective toner images by reversing the relationship between the first toner image and the second toner image.
According to a fifth aspect of the present invention, there is provided the image forming apparatus according to the second aspect, wherein the image forming apparatus includes the first image according to an average image density of a toner image included in the image information or calculated based on the image information. The toner image forming means is configured to form the respective toner images by reversing the relationship between one toner image and the second toner image.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the second to fifth aspects, the reversing means for reversing the front and back of the recording medium after passing through the fixing means, and the fixing means after passing through the fixing means. The present invention is characterized in that there is provided a conveyance path switching means for switching the conveyance path of the recording body between a path that reverses the front and back and a path that is not reversed.
According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the second to sixth aspects, the transfer unit is configured to change the transfer current in accordance with the image information. It is.
According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the second to seventh aspects, the surface of the toner image carrier in the front transfer portion and the first surface in contact with the surface in accordance with the image information. The transfer means is provided with contact pressure changing means for changing the contact pressure.
According to a ninth aspect of the present invention, in the image forming apparatus according to the eighth aspect, the contact pressure changing means that changes the contact pressure using the rotation of an eccentric cam is used. is there.
According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the second to seventh aspects, the surface of the toner image carrier in the front transfer portion and the first surface in contact with the surface in accordance with the image information. The transfer means is provided with contact area changing means for changing the contact area.
The invention according to claim 11 is the image forming apparatus according to claim 10, wherein the toner image carrier is a toner carrying belt that is endlessly moved while being stretched by a plurality of tension members, and the contact area. As the changing means, a member that changes the contact area by moving the tension member to change the tension posture of the toner carrying belt is used.
According to a twelfth aspect of the present invention, in the image forming apparatus according to any one of the seventh to eleventh aspects, at least two of the transfer current, the contact pressure, and the contact area are changed independently of each other. It is a feature.
According to a thirteenth aspect of the present invention, in the image forming apparatus according to any one of the first to twelfth aspects, a toner storage unit that stores toner used in the toner image forming unit is provided, and the weight average particle diameter is 3 to 8 [ μm] and a toner having a weight average particle size divided by a number average particle size of 1.00 to 1.40 is stored in the toner storage unit.

In these image forming apparatuses having the configuration according to claim 1, in the front transfer unit, the conductive member is brought into contact with the second toner image carrier without contacting the second surface of the recording body. Further, the second toner image carrier is not interposed between the first toner image carrier and the conductive member in which the recording body is sandwiched. For this reason, the transfer current varies in the direction of the recording material surface between the first toner image carrier and the conductive member due to the difference in density of the second toner image carried on the second toner image carrier and the presence of image portions. Avoid the situation. As a result, transfer failure of the first toner image in the front transfer portion can be suppressed.
According to the second aspect of the present invention, when it is found that the density difference or the image portion dot distribution of the second toner image is larger than that of the first toner image based on the image information, the first toner Each toner image can be formed by reversing the relationship between the image and the second toner image. When the respective toner images are formed in this way, a toner image having a smaller density difference or image portion dot degree out of the two toner images is formed as the second toner image, and the density of the second toner image is determined. It is possible to suppress the transfer failure of the first toner image due to the difference or the dot portion.

A first embodiment in which the present invention is applied to an electrophotographic color copying machine (hereinafter simply referred to as a copying machine) as an image forming apparatus will be described below.
FIG. 4 is a schematic configuration diagram showing the copying machine according to the first embodiment. In this figure, the copier has a printer unit 100, an operation / display unit 90, a paper feeding device 40, an automatic image reading device 200, a paper supply device 300, and the like.

  The printer unit 100 includes a first image forming unit disposed above and a second image forming unit disposed below the paper conveyance path 43A. The first image forming unit includes a first transfer unit 20 having a first intermediate transfer belt 21 that moves endlessly in the direction of the arrow in the drawing. Further, the second image forming unit includes a second transfer unit 30 having a second intermediate transfer belt 31 that moves endlessly in the direction of the arrow in the drawing. Four first process units 80Y, 80M, 80C, and 80K are arranged above the upper stretched surface of the first intermediate transfer belt 21. On the other hand, four second process units 81Y, 81M, 81C, and 81K are arranged on the side of the side tension surface of the second intermediate transfer belt 31. The subscripts Y, M, C, and K attached to the numbers of the first and second process units indicate the colors of toner to be handled. The same subscript is attached to each device in the process unit.

  Each process unit (80Y, M, C, K, 81Y, M, C, K) has a photoreceptor (1Y, M, C, K) as a latent image carrier. The photoreceptors 1Y, 1M, 1C, and 1K of the first process units 80Y, 80M, 80M, 80K, 80K, 80K, 80K, and 80K are arranged at regular intervals, and at least at the time of image formation, contact the upper stretched surface of the first intermediate transfer belt 21, respectively. Hereinafter, the belt surface that contacts in this way is referred to as a first image receiving surface.

  On the other hand, the photoreceptors 1Y, 1M, 1C, and 1K of the second process units 81Y, 81M, 81C, and 81K are also arranged at equal intervals, and at least at the time of image formation, contact the upper stretched surface of the second intermediate transfer belt 21, respectively. . Hereinafter, the belt surface that contacts in this way is referred to as a second image receiving surface.

  The first intermediate transfer belt 21 is stretched by a plurality of rollers in a horizontally long posture with a space in the horizontal direction rather than in the vertical direction, and in a posture in which the first image receiving surface extends substantially horizontally. The first process units 80Y, 80M, 80C, and 80K are arranged in parallel so as to be in contact with the substantially horizontal first image receiving surface.

  On the other hand, the second intermediate transfer belt 31 is in a vertically long posture with a plurality of rollers to take a space in the vertical direction rather than in the horizontal direction, and the second image receiving surface is inclined in a posture to be inclined from the upper left to the lower right in the drawing. It is built. The second process units 81Y, 81M, 81C, 81K are in contact with the second image receiving surface inclined in this way, on the left side of the second intermediate transfer belt 31 in the drawing, from the upper left to the lower right in the drawing. It is arrange | positioned so that it may become a diagonal arrangement | sequence.

  FIG. 5 is an enlarged configuration diagram showing one of the four first process units 80Y, 80M, 80C, 80K. The four first process units 80Y, 80M, 80C, 80K, 80K, 80K, 80K, 80K, 80K, 80K, Y80, Y80, 80K, 80K, Y80, Y80, 80K, 80K, Y80, Y80, 80K The subscript K is omitted. In the figure, the photosensitive member 1 is driven to rotate counterclockwise in the drawing by a driving means (not shown) during operation of the printer unit (100). Around the photosensitive member 1, there are an image forming member such as a scum tron charger 3, an exposure device 4, a developing device 5, a cleaning device 2 and a photostatic device Q as a charging means, a potential sensor S1, an image sensor S2, and the like. It is arranged.

  The drum-shaped photoreceptor 1 is formed by coating 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. An amorphous silicon (a-Si) layer may be coated. Further, it may be a belt shape instead of a drum shape.

  The cleaning device 2 includes a cleaning brush 2a, a cleaning blade 2b, a recovery member 2c, and the like, and removes and recovers transfer residual toner remaining on the surface of the photoreceptor after passing through a primary transfer nip described later.

  The scumtron charger 3 is for uniformly charging the surface of the photoconductor 1 that is rotationally driven to, for example, a negative polarity. As a charging means for performing such uniform charging, a camtron charger may be used instead of the scumtron charger. Alternatively, a charging bias member to which a charging bias is applied may be in contact with the surface of the photoreceptor 1.

  The exposure device 4 optically scans the surface of the uniformly charged photoreceptor 1 with light generated based on image data corresponding to one of the colors, and an electrostatic latent image is formed on the surface of the photoreceptor 1. Form. In the example shown in the figure, the exposure device 4 is composed of an LED (light emitting diode) array and an imaging element. A laser scanning method using a light beam modulated according to image data to be formed using a laser light source, a polygon mirror, or the like may be used.

  The developing device 5 is of a two-component developing system that develops an electrostatic latent image on the photoreceptor 1 using a two-component developer containing toner and a magnetic carrier. The two-component developer is conveyed in the depth direction in the figure while being agitated by two conveying screws 5c. The developer conveying directions of these two conveying screws 5c are opposite to each other. For example, if the developer conveying direction of the left conveying screw 5c in the figure is the front side from the back side in the figure, the developer conveying direction of the right conveying screw 5c in the figure is the front side to the back side in the figure. The two-component developer transported to the end in the depth direction of the developing device 5 by the former transport screw 5c is transferred to the latter transport screw 5c. Then, in the process of being stirred and conveyed from the end portion toward the opposite end portion, a part is carried on the developing roll 5b described later. Further, the two-component developer that is not carried or returned from the developing roll 5b to the right conveying screw 5c is delivered to the left conveying screw 5c at the opposite end. In this way, the two-component developer is circulated and conveyed in the developing device 5. As the developing device 5, a one-component developing system using a one-component developer containing toner as a main component without including a magnetic carrier may be used.

  The developing roll 5a is a non-magnetic cylinder made of stainless steel, aluminum, or the like, and has a sleeve that is driven to rotate clockwise in the drawing by a driving means (not shown), and a magnet roller that is internally fixed so as not to rotate. is doing. The magnet roller has a plurality of magnetic poles divided in the circumferential direction inside the sleeve. The two-component developer conveyed by the conveyance screw 5c on the right side in the drawing is attracted by the magnetic force generated by the magnet roller, and is pumped up on the surface of the sleeve that is rotationally driven. Then, prior to being transported to the developing area facing the photoreceptor 1 along with the sleeve surface, it passes through a regulation position that is a position facing the blade 5b.

  The blade 5b is disposed so that its tip is close to the sleeve surface through a predetermined gap. Then, when the two-component developer on the sleeve surface passes through the regulation position immediately below, the thickness of the two-component developer is regulated to a predetermined size.

  The two-component developer whose layer thickness is regulated in this way is conveyed to a developing region that is a position facing the photoreceptor 1 as the sleeve rotates. The electrostatic latent image formed by attenuating the charge by optical scanning on the surface of the photoreceptor 1 uniformly charged to the negative polarity is rubbed against the two-component developer on the sleeve surface in the development region. . Then, it is developed into one of Y, M, C, and K colors by the adhesion of negatively chargeable toner having the same polarity as the latent image. In the first process unit 80, so-called reversal development is performed. As a result, a toner image of any one of Y, M, C, and K is formed on the photoreceptor 1.

  The two-component developer that has consumed toner in the developing region returns to the developing device 5 as the sleeve rotates. Then, under the influence of the repulsive magnetic field formed by the magnetic poles of the same polarity and adjacent to each other of the magnet roller, the magnet roller is separated from the sleeve surface and returned to the right conveying screw 5c in the drawing, and then the left side in the drawing. It is delivered to the conveying screw 5c.

  A toner concentration sensor 5e is disposed below the left conveying screw 5c in the drawing, and detects the magnetic permeability of the two-component developer conveyed by the left conveying screw 5c. Since the magnetic permeability of the two-component developer has a correlation with the toner density, the toner density sensor 5e detects the toner density.

  When the control unit (not shown) determines that the toner density of the two-component developer is less than a predetermined target density value based on the output signal from the toner density sensor 5e, of the two toner supply units (not shown), The one corresponding to the component developer is driven for a predetermined time. These eight toner supply units are respectively provided for four developing devices of the first process unit (80Y, M, C, K) or four developing devices of the second process unit (81Y, M, C, K). It corresponds to any one. It is connected to one of the four Y, M, C, and K toner bottles (86Y, M, C, and K in FIG. 4) that are detachably set in the bottle storage unit 85 in the upper part of the printer unit (100). . Then, the toner of a predetermined color is supplied from the connected toner bottle onto the conveying screw 5c on the left side in the drawing in the corresponding developing device. As a result, the toner concentration of the two-component developer that has consumed the toner by the development is recovered. As the toner supply means having such a configuration, a method of sucking the toner in the toner bottle and transporting it to the inside of the developing device with a suction force by a conventionally known Mono pump is preferable. According to this method, there are few restrictions on the installation location of the toner bottle, which is advantageous for space allocation inside the printer unit (100). Further, since the toner can be replenished in a timely manner, it is not necessary to provide a large toner storage space in the developing device 5, and the developing device 5 can be downsized.

  FIG. 6 is an enlarged configuration diagram showing one of the four second process units (81Y, M, C, K). Since the four second process units (81Y, M, C, K) have almost the same configuration except that the colors of the toners to be handled are different, the second process unit 81 includes the first process unit (81Y, M, C, K). 80) and the constituent members are the same, but the rotation direction of the photoreceptor 1 is different. However, they are mutually shaped with respect to the y-axis passing through the rotation axis 1a of the photoreceptor 1. Although this shape is related to the arrangement of members provided around the photoreceptor 1, it is an important matter. Specifically, consideration is given to a method of connecting a connecting portion with the main body of the printer unit 100, for example, a connecting portion with a driving means, an electrical connecting portion, a toner supplying portion, and a toner discharging portion. Thereby, the first process unit (80Y, M, C, K) and the second process unit (81Y, M, C, K) can be made compatible. Accordingly, it is not necessary to separately manufacture the developing device, the cleaning device, and the parts for the first process unit and the second process unit, so that the efficiency in manufacturing parts and managing parts is high, and the overall cost can be reduced. it can.

  In FIG. 4 described above, the first image forming unit includes a plurality of first process units (80Y, M, C, K) and a first transfer unit 20. Further, the second image forming unit includes a plurality of second process units (81Y, M, C, K) and a second transfer unit 30. In the printer unit 100, the first transfer unit 20 and the second transfer unit 30 constitute a double-side transfer device.

  In the first transfer unit 20, the first intermediate transfer belt 21 is stretched by a plurality of rollers 22 (four), 23, 24, 25, 26 (two), 27, 28, 29, and the first process unit. 80 Y, M, C, and K photoconductors 1 Y, M, C, and K are brought into contact with each other. By this contact, the first transfer unit 20 causes the Y, M, C, and K toner images (hereinafter also referred to as single-color first toner images) on the photoreceptors 1Y, 1M, 1C, and 1K to be transferred to the first intermediate transfer belt 21. A primary transfer nip for Y, M, C, and K to be superimposed and transferred is formed. The first intermediate transfer belt 21 is endlessly moved clockwise in the figure while forming these four primary transfer nips. In each primary transfer nip, any one of the four primary transfer rollers 22 to which a primary transfer bias is applied by a power source (not shown) is placed between the photoreceptors 1Y, M, C, and K and the first intermediate transfer belt 21. Is sandwiched. Due to the influence of the primary transfer bias and the nip pressure, a single monochrome first toner image is primarily transferred onto the first intermediate transfer belt 21 at each primary transfer nip. By this superposition, a first toner image of another color is formed on the first intermediate transfer belt 21 that is an image carrier.

  A cleaning device 20 </ b> A is provided on the outer periphery of the first intermediate transfer belt 21 at a position facing the roller 23. The cleaning device 20 </ b> A wipes off the transfer residual toner remaining on the surface of the first intermediate transfer belt 21 after passing through each primary transfer nip and foreign matters such as paper dust. Members related to the first intermediate transfer belt 21 are integrally formed as the first transfer unit 20 and can be attached to and detached from the printer unit 100.

  On the other hand, in the second transfer unit 30, the second intermediate transfer belt 31 is stretched by a plurality of rollers 32 (four), 33, 34, 35, and 36 (two), and the photoreceptors 1Y, 1M, 1C, and 1K. Is in contact with By this contact, the second transfer unit 30 transfers the Y, M, C, and K second toner images (hereinafter also referred to as single-color second toner images) on the photoreceptors 1Y, 1M, 1C, and 1K to the second intermediate transfer. A primary transfer nip for Y, M, C, and K to be superimposed and transferred on the belt 31 is formed. The second intermediate transfer belt 31 moves endlessly counterclockwise in the figure while forming these four primary transfer nips. In each primary transfer nip, any one of the four primary transfer rollers 32 to which a primary transfer bias is applied by a power source (not shown) is placed between the photoreceptors 1Y, M, C, and K and the second intermediate transfer belt 31. Is sandwiched. Due to the influence of the primary transfer bias and the nip pressure, the Y, M, C, and K second toner images are primarily transferred onto the second intermediate transfer belt 31 at each primary transfer nip. By this superposition, a second toner image of another color is formed on the second intermediate transfer belt 31 that is an image carrier.

  A cleaning device 30 </ b> A is provided on the outer periphery of the second intermediate transfer belt 31 at a position facing the roller 33. The cleaning device 30A wipes off unnecessary toner remaining on the surface of the intermediate transfer belt 31 after passing through each primary transfer nip and foreign matters such as paper dust. Members related to the second intermediate transfer belt 31 are also integrally formed as the second transfer unit 30 and can be attached to and detached from the printer unit 100.

Each of the two intermediate transfer belts (21, 31) is a belt having a base made of a resin film or rubber having a base thickness of 50 to 600 [μm], for example. The toner image, which is a visible image carried on the photosensitive member 1, has an electric resistance value that enables electrostatic transfer to the belt surface by the primary transfer bias applied to the primary transfer rollers (22, 32). Demonstrate. As an example of such an intermediate transfer belt, a material in which carbon is dispersed in polyamide and the volume resistance value is adjusted to about 10 ⁶ to 10 ¹² [Ωcm] can be exemplified. Belt detent ribs for stabilizing the running of the belt are provided on one side or both ends of the belt. The circumference of the belt is about 1500 [mm].

As the four primary transfer rollers 22 as the primary transfer means of the first transfer unit 20 and the four primary transfer rollers 32 as the primary transfer means of the second transfer unit 30, for example, those having the following configurations are used. Can be used. That is, the surface of a metal roller as a core metal is coated with a conductive rubber material, and a bias is applied to the core metal part from a power source (not shown). In the first embodiment, a conductive rubber material obtained by dispersing carbon in urethane rubber is used, and the volume resistance is adjusted to about 10 ⁵ Ωcm.

  The printer unit 100 can also output a monochrome image using only K toner. When outputting a monochrome image, the Y, M, C process units 80Y, 80M, 80C in the first transfer unit 20 are not used. In addition to not operating the process units 80Y, 80M, and 80C, a mechanism is provided for keeping them in contact with the first intermediate transfer belt 21. An internal frame (not shown) that supports the roller 26 and the primary transfer roller 22 is provided, and is supported so as to be rotatable about a certain point. Then, by rotating in a direction away from the photosensitive member, only the photosensitive member 1K is brought into contact with the first intermediate transfer belt 21, and an image forming process is executed to create a monochrome image using black toner. Such a configuration is advantageous in terms of improving the life of the photoreceptor. Similarly, the second transfer unit 30 is configured to retract the process units 81Y, 81M, and 81C from the second intermediate transfer belt 31 when outputting a monochrome image.

  On the outer periphery of the first intermediate transfer belt 21, the transfer roller 46 sandwiches the first intermediate transfer belt 21 between the transfer counter roller 28 that stretches while supporting the first intermediate transfer belt 21 on the back surface. It is arranged. Thereby, in the first transfer unit 20, a secondary transfer nip in which the first intermediate transfer belt 21 and the transfer roller 46 come into contact with each other is formed. A region from the transfer counter roller 28 through the secondary transfer nip to the transfer roller 46 is a front transfer unit in the double-side transfer device.

The transfer roller 46 is obtained by coating the surface of a metal roller serving as a core metal with a conductive rubber, and a secondary transfer bias is applied to a core metal portion from a secondary transfer bias power source (not shown). The conductive rubber has a volume resistance adjusted to about 10 ⁷ Ωcm by carbon dispersion.

  A registration roller pair 45 is disposed on the right side of the secondary transfer nip in the drawing. The registration roller pair 45 temporarily suspends the rotation of both rollers after the transfer paper P sent from the paper feeding device 40 disposed on the right side of the printer unit 100 in the drawing is sandwiched between the rollers. Then, the transfer paper P is sent out toward the secondary transfer nip at a timing that can be synchronized with the four-color toner image that is the superimposed toner image on the first intermediate transfer belt 21. The transferred transfer paper P has a four-color toner image brought into close contact with a first surface (a surface facing the upper side in the drawing) which is one surface of the transfer paper P at the secondary transfer nip. The four-color toner images on the first intermediate transfer belt 21 are secondarily transferred collectively onto the first surface under the influence of the secondary transfer bias and the nip pressure. The transfer paper P that has passed through the secondary transfer nip is separated from the first intermediate transfer belt 21 and the transfer roller 46 and transferred to the second intermediate transfer belt 31.

  In the second transfer unit 30, a belt-wrapped portion by the upper stretching roller 34 that stretches the second intermediate transfer belt 31 is an upper stretched surface of the second intermediate transfer belt 31. Above this upper stretch surface, a transfer charger 47, which is a charge applying means, is disposed so as to face the upper stretch surface with a predetermined gap. A region from the transfer charger 47 to the upper stretching roller 34 via this predetermined gap is a rear transfer portion of the second transfer unit 30.

  The transfer charger 47 is a known type, and a thin wire of tungsten or gold is used as a discharge electrode, held by a casing, and a transfer current is applied to the discharge electrode from a power source (not shown). While passing the transfer paper P between the second intermediate transfer belt 31 and the transfer charger 47, the four-color toner on the second intermediate transfer belt 31 is applied to the first surface with an electric charge generated from the transfer charger 47. The image is secondarily transferred collectively onto the second surface of the transfer paper P. Both the secondary transfer bias and the charge applied by the transfer charger 47 have a positive polarity opposite to the polarity of the toner.

  On the right side of the printer unit 100 in the drawing, a paper feeding device 40 that accommodates transfer paper P is provided. The paper feeding device includes a plurality of paper storage means. Specifically, the uppermost sheet feed tray 40a, the first sheet feed cassette 40b disposed below the sheet feed tray 40a, the second sheet feed cassette 40c disposed below the first sheet feed cassette 40b, and the lower section thereof Is provided with a third paper feed cassette 40d. Each of these paper storage means is disposed so as to be able to be drawn out to the near right side (operation surface side) with respect to the paper surface. In addition, transfer sheets P of different sizes are accommodated. In each paper storage means, the uppermost transfer paper P is selectively fed and separated by the corresponding paper feeding / separating means 41A to 41D, and only one sheet is reliably fed by the plurality of conveying roller pairs 42B to the paper conveying path 43B. And sent to 43A.

  The paper transport path 43A is provided with a pair of registration rollers 45 for taking a feeding timing for feeding the transfer paper P to the front transfer unit and the rear transfer unit of the double-side transfer device. Further, a lateral registration correction mechanism 44 for setting a position perpendicular to the conveyance direction of the transfer paper P to a normal position is provided in the paper conveyance path 43A. Examples of the lateral registration correcting mechanism 44 include the following. In other words, the transfer sheet P is slid and conveyed so that the transfer sheet P is composed of a reference guide and a skew cam pair (not shown) and presses the end of the transfer sheet in the horizontal direction against the reference guide. Then, the transfer paper is aligned with a predetermined position. The reference guide is moved and arranged at a predetermined position according to the size of the transfer paper P. The lateral registration correction mechanism 44 regulates the transfer paper P to be aligned at a predetermined position by pressing both sides of the transfer paper P for a short time and a plurality of times from both lateral directions of the transfer paper P with respect to the transfer direction of the transfer paper P. A jogger system composed of members may be used.

  The transfer sheet P is conveyed from the registration roller pair 45 toward the preceding transfer section where the secondary transfer nip is formed by the contact between the first intermediate transfer belt 21 and the transfer roller 46. Thereafter, the second intermediate transfer belt 31 and the transfer charger 47 are sent toward the rear transfer portion where they face each other.

  In the paper feeding device 40, the transfer paper P discharged from the uppermost paper feeding tray 40 a among the plurality of paper feeding trays is bent with respect to the paper conveyance path 43 </ b> A of the printer unit 100. It is transported almost horizontally and straight. Therefore, even thick transfer paper P or highly rigid paperboard can be reliably fed into the paper transport furnace 43A of the printer unit 100 if it is accommodated in the paper feed tray 40a. In addition, it is convenient to adopt an air sheet feeding composed of a vacuum mechanism so that the sheet feeding tray 40a can reliably feed a transfer sheet having various characteristics. Although not shown, a sensor for detecting the transfer paper P is provided at a key point of the paper transport path 43A, and serves as a trigger for various signals based on the presence of the transfer paper P.

  A second paper feed path 43C is provided above the uppermost paper feed tray 40a. The transfer paper P can be supplied to the second paper feed path 43C from the second paper feed device 300 installed on the right side of the paper feed device 40 in the drawing.

  On the left side of the second transfer unit 30 in the figure, a paper transport unit 50 that moves the paper transport belt 51 endlessly counterclockwise while stretching the paper transport belt 51 by a plurality of stretching rollers 52, 53, 54, 55, 56. Is arranged. The paper transport belt 51 is arranged on the paper transport belt 51 at a position where the transfer paper P discharged from the rear transfer portion of the second transfer unit 30 is wound around by a receiving roller 52 which is one of a plurality of stretching rollers. To receive. Charge is applied to the front surface of the paper transport belt 51 by the electrostatic adsorption charger 57 at a timing earlier than the reception. By applying this charge, the paper transport unit 50 can electrostatically attract the transfer paper P discharged from the subsequent transfer section to the front surface of the paper transport belt 51.

  The paper conveyance belt 51 having the transfer paper P electrostatically adsorbed on the front surface conveys the transfer paper P from the right side to the left side in the drawing along with the endless movement thereof. Then, the transfer paper P is delivered to the fixing device 60 as fixing means disposed on the left side of the paper transport unit 50 in the drawing. Charge is applied by the separation charger 58 to the transfer paper P that is electrostatically attracted to the front surface of the paper transport belt 51 at a timing earlier than this delivery. By applying this electric charge, the transfer paper P that has been electrostatically attracted to the front surface of the paper transport belt 51 until then is easily separated from the belt. Of the plurality of stretching rollers, a belt that suddenly changes the moving direction in accordance with the curvature of the separation roller 54 at a belt winding position by the separation roller 54 disposed closest to the fixing device 60. The transfer paper P is separated from the paper and transferred to the fixing device 60.

  As the fixing device 60, a system having a heater inside the fixing roller, a system in which a belt to be heated is run, a system using induction heating, or the like can be used. In the figure, a fixing nip formed by abutting two fixing rollers is used to fix the first toner image of the other color and the second toner image of the other color by heating the transfer paper P from both sides. Adopted. In order to make the color tone and glossiness of the images on both sides of the transfer paper P the same, the belt material, hardness, surface property, etc. of the two fixing rollers are the same up and down. Further, various parameters of the fixing device 60 are controlled so as to create an optimal fixing condition for each surface depending on whether it is a full-color image and a monochrome image, or one surface or both surfaces.

  The transfer paper P that has been subjected to the fixing process by the fixing device 60 is sent out toward the discharge path. In this discharge path, a cooling roller pair 70 having a cooling function is disposed for the purpose of cooling the transfer paper P after the fixing process and stabilizing the unstable toner state at an early stage. As the cooling roller pair 70, a heat pipe structure roller having a heat radiating portion can be adopted. The transfer paper P cooled by the cooling roller pair 70 is discharged and stacked by a discharge roller pair 71 on a discharge stack unit 75 provided on the left side of the printer unit 100. This discharge stacking unit employs a mechanism in which a receiving member moves up and down according to a stack level by an elevator mechanism (not shown) so that a large amount of transfer paper can be stacked. Note that the transfer paper can also be transported to another post-processing apparatus through the paper discharge stack section 75. As another post-processing apparatus, an apparatus for bookbinding such as punching, cutting, folding, and binding can be provided.

  On the upper surface of the printer unit 100, toner bottles 86Y, 86M, 86C, and 86K of each color in which unused toner is stored are detachably stored in the bottle storage unit 85. The bottle housing portion 85 is on the back side when viewed from the operation direction on the upper surface of the printer unit 100, and a flat surface portion is secured on the front side of the upper surface of the printer unit 100, so that it can be used as a work table. The toner supply means described above supplies toner to each developing device as necessary. In the first embodiment, the first image forming unit and the second image forming unit disposed above and below supply toner from a common toner bottle to a developing device that handles toner of the same color. It can be separated. The toner bottle 86K for black toner that is highly consumed can have a particularly large capacity.

  The operation / display unit 90 provided on the upper surface of the printer unit 100 is provided with an input operation unit (not shown) including a keyboard and the like, thereby inputting conditions for image formation. In addition, various types of information can be displayed on a display unit (not shown) such as a display, so that information exchange between the operator and the printer unit 100 is facilitated.

  A waste toner storage unit 87 provided in the printer unit 100 is connected to the cleaning device 2, the intermediate transfer belt cleaning devices 20A and 30A, and the like. Then, foreign substances such as waste toner and paper dust sent from these are collected and stored in a lump. Since these cleaning devices (2, 20A, 30A, and 50A) do not include a large-capacity waste toner storage unit, the cleaning device can be reduced in size, and the waste toner disposal operability is good. A full sensor (not shown) is used to issue a warning such as toner disposal in the waste toner storage unit 87 or container replacement.

  Various power supplies, control boards, and the like are protected and housed in a sheet metal frame in a control unit 95 provided in the printer unit 100. The inside of the image forming apparatus becomes hot due to heat from the fixing device 60 or heat generated from the electrical device. However, as a countermeasure against this, a fan F is provided to prevent deterioration of the function due to heat of the internal members. The fan F is coupled to the heat radiating portion of the cooling roller pair 70 to ensure the cooling effect of the cooling roller pair 70.

  An automatic image reading device (ADF) 200 that reads an image of a document while automatically conveying the document by a well-known technique is provided on the upper portion of the paper feeding device 40, and reading information obtained by this is sent to the control unit 95. . Based on the sent read information, the printer unit 100 is driven and controlled, and the same image as the original is output. Further, image information from a personal computer (not shown) or the like can be sent to the printer unit 100 and an image corresponding to the image information can be output. Furthermore, it is also possible to send image information sent from a telephone line (not shown) and output an image corresponding to the image information. As described above, the second paper supply device 300 that supplies the transfer paper P to the paper supply device 40 is disposed on the right side of the paper supply device 40 in the drawing.

Next, an operation at the time of single-sided recording in which the printer unit 100 forms a full-color image on one side of the transfer paper 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 in which the four-color toner images transferred to the first intermediate transfer belt 21 are collectively transferred onto the first surface of the transfer paper P. Another method is a method in which the four-color toner image transferred to the second intermediate transfer belt 31 is secondarily transferred onto the second surface of the transfer paper P at once. Hereinafter, the former method will be described as an example.

  When the printer unit 100 is operated, the first intermediate transfer belt 21 and the photoreceptors 1Y, 1M, 1C, and 1K in the first process units 80Y, 80M, 80C, 80K rotate. At the same time, the second intermediate transfer belt 31 moves endlessly, but the photosensitive members 1Y, M, C, and K in the second process units 81Y, 81M, 81C, and 81K are separated from the second intermediate transfer belt 31 and are not rotated. Is done. Then, image formation by the first process 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.

  The electrostatic latent image is developed into a Y toner image by the developing device of the first process unit 81Y for Y, and is electrostatically primary-transferred onto the first intermediate transfer belt 21 at the primary transfer nip for Y. The Such latent image formation, development, and primary transfer operations are sequentially performed in the same manner on the photoconductors 1M, 1C, 1K, and K side. Then, the M, C, and K toner images are sequentially superimposed on the Y toner image on the first intermediate transfer belt 21 at the primary transfer nip for M, C, and K, and are primarily transferred. A four-color toner image is formed on the first intermediate transfer belt 21 by this superimposing primary transfer.

  On the other hand, the paper feeding device 40 sends out transfer paper corresponding to the image data from the internal paper feeding tray 40a or the paper feeding cassettes 40bc, 40bc, d by any one of the paper feeding / separating means 41A, B, C, D. . And it conveys toward the paper conveyance path 43C of the printer part 100 by conveyance roller pair 42B, 42C. Then, it is sent to the lateral registration correction mechanism 44.

  The lateral registration correction mechanism 44 adjusts the inclination of the posture of the transfer sheet P in the middle of being conveyed from the paper feeding device 40 serving as the recording medium supply unit toward the double-sided transfer device (first and second transfer units) from the conveyance direction. It is an inclination correction means for correcting. A pair of guide plates arranged in the paper surface direction orthogonal to the transport direction on the upstream side of the registration roller pair 45 is abutted against both ends orthogonal to the transport direction of the transfer paper P, so that the posture of the transfer paper P is adjusted. Correct the tilt. The two guide plates of the pair of guide plates are movable in the direction of the paper surface orthogonal to the transport direction. By moving according to the width of the fed transfer paper P, the distance between the plates can be reduced. Can be adjusted to the width.

  The transfer paper P whose posture inclination is corrected by the lateral registration correction mechanism 44 reaches between the rollers of the registration roller pair 45, and is timed and sent to the preceding transfer section. Then, the four-color toner images on the first intermediate transfer belt 21 are secondarily transferred onto the first surface at the secondary transfer nip of the preceding transfer unit. The transfer residual toner is cleaned on the front surface of the first intermediate transfer belt 21 that has passed through the secondary transfer nip by the belt cleaning device 20A.

  In each of the first process units 80Y, 80M, 80C, 80K, the transfer residual toner remaining on the photoreceptors 1Y, 1M, 1C, 1K after passing through the primary transfer nip is cleaned by the cleaning device (2). Is done. As shown in FIG. 5, the cleaning device (2) removes transfer residual toner from the first intermediate transfer belt 21 by the cleaning brush 2a and the cleaning blade 2b. The removed foreign matter such as toner is sent to the collecting unit 87 by the collecting unit 2c. 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. Further, the surface of the photoreceptor 1 after cleaning is initialized by removing the residual charges by the static eliminating device Q.

  The transfer paper on which the four-color toner image is secondarily transferred onto the first surface at the secondary transfer nip of the front transfer unit is transferred to the second intermediate transfer belt 31 of the second transfer unit 30, and then the paper transport unit 50. Sent to. Then, the paper is transferred from the paper transport unit 50 to the fixing device 60. Prior to this transfer, the transfer paper P is charged by the separation charger 58. With this application, the transfer paper that has been electrostatically attracted to the second intermediate transfer belt 31 can be easily separated from the belt.

  In the fixing device 60, each color toner in the full-color image carried on the first surface of the transfer paper P is melted and mixed by heating. Since the transfer paper P has toner only on its first side, less heat energy is required for fixing compared to double-sided recording with toner on both sides. The control unit 95 optimally controls the power used by the fixing device 60 according to the image. Even after the fixing process is performed, until the toner image is completely fixed on the transfer paper P, the toner image is rubbed against a guide member or the like in the conveyance path, and the image is lost or distorted. In order to prevent this problem, the transfer paper that has passed through the fixing device 60 is provided with a pair of cooling rollers 70 as cooling means.

  In the present copying machine, since the image forming order is programmed so that the transfer sheets of the young pages are sequentially stacked on the discharge stack unit 75, the page order is aligned in the stack unit 75. Since the discharge stacking unit 75 is lowered as the number of transfer sheets P to be discharged increases, the transfer sheets can be stacked in an orderly and reliable manner, and the page order is not disturbed. Instead of directly stacking the recorded transfer paper on the paper discharge stack section 75, a punching process can be performed, or the transfer paper can be conveyed to a post-processing device such as a sorter, a collator, a binding device, or a folding device.

  In another method for forming an image on one side of the transfer paper P, image data of a young page is not used for page alignment because the image is not formed in the first process units 80Y, 80M, 80C, 80K. The difference is that images are formed sequentially. However, the description is omitted because 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 transfer paper will be described.
When an image signal is input to the printer unit 100, Y, M, C, K toners are applied to the photoreceptors 1Y, M, C, K of the first process units 80Y, 80M, 80C, 80K described in the single-side recording operation. An image is formed. These are primary-transferred by being sequentially superimposed on the first intermediate transfer belt 21 at the primary transfer nips for Y, M, C, and K. Almost in parallel with this step, Y, M, C, and K toner images are formed on the photoreceptors 1Y, M, C, and K of the second process units 81Y, 81M, 81C, and 81K. These are primarily transferred onto the second intermediate transfer belt 31 in sequence by primary transfer nips for Y, M, C, and K. In this way, four-color toner images are formed on the first intermediate transfer belt 21 and the second intermediate transfer belt 31, respectively.

  The unit intervals of the second process units 81Y, 81M, 81C, 81K are smaller than the unit intervals of the first process units 80Y, 80M, 80C, 80K. As a result, the second transfer unit 30 completes the primary transfer with superimposition faster than the first transfer unit 20.

  The four-color toner image on the first intermediate transfer belt 21 is secondarily transferred onto the first surface of the transfer paper P which is timed and sent from the registration roller pair 45 to the secondary transfer nip of the preceding transfer unit. Then, it is delivered to the latter transfer section. Then, the four-color toner image on the second intermediate transfer belt 31 is secondarily transferred to the second surface at the rear transfer portion where the second intermediate transfer belt 31 and the transfer charger 47 face each other with a predetermined gap. Is done.

  The transfer paper P having the full-color image formed on both sides in this way is delivered to the fixing device 60 via the paper transport unit 50. Then, a fixing process by heating or pressurization is performed in the fixing device 60, and the toner images on both sides are respectively melted and mixed. Further, after passing through the cooling roller pair 70 and the paper discharge roller 71, the paper is discharged onto the paper discharge stack 75.

  When double-sided recording is performed on a plurality of pages of transfer paper, the image forming order is controlled so that the image of the young page becomes the bottom surface and is stacked on the paper discharge stack unit 75. As a result, when the paper is taken out from the paper discharge stack 75 and the top and bottom surfaces are reversed, the recorded matter is one page in order from the top, the second page on the back, the third page on the second sheet, and the fourth page on the back. Such control of image forming sequence and control such as increasing the power input to the fixing device compared to the one-side recording are executed by the control unit 95.

  Although an example in which full-color recording is performed regarding the single-sided recording operation and the double-sided recording operation has been described, monochrome recording using only black toner is also possible. When the need for maintenance or replacement of parts arises, maintenance is performed by opening an unillustrated exterior cover or the like.

  In the copying machine configured as described above, the combination of the first image forming unit and the control unit 95 described above allows the multicolor first toner image as the first toner image on the surface of the first intermediate transfer belt 21 as the first toner image carrier. A first toner image forming unit for forming one toner image is configured. A second toner image that forms a multi-color second toner image as a second toner image on the surface of the second intermediate transfer belt 31 as a second toner image carrier by a combination of the second image forming unit and the control unit 95. A forming part is configured. In addition, a toner image forming unit is configured by a combination of the first image forming unit, the second image forming unit, and the control unit 95. The first toner image is a first toner image of another color obtained by superimposing a plurality of single-color first toner images, and a toner image composed of only a single-color first toner image of Y, M, C, or K. It is a generic name. The second toner image is a second toner image of another color obtained by superimposing a plurality of single-color second toner images, and a toner image including only a single-color second toner image of any one of Y, M, C, and K. It is a generic name.

  The first image forming unit and the second image forming unit express gradations according to the density of dots that are toner-attached pixels that are pixels to which toner is attached among the pixels constituting the toner image. Therefore, in the halftone portion or highlight portion of the toner image, a certain amount of space is provided between each dot or between dot units formed by a set of a predetermined number of dots.

Next, a characteristic configuration of the copying machine according to the first embodiment will be described.
FIG. 7 is an enlarged configuration diagram illustrating the front transfer unit and the rear transfer unit of the copying machine in an enlarged manner. The transfer paper P sent out from a pair of registration rollers 45 (not shown) enters the preceding transfer section where the transfer facing roller 28 and the transfer roller 46 are opposed to each other. Then, the secondary transfer formed by contact between the first intermediate transfer belt 21 backed up by the transfer counter roller 28 connected to the ground and the transfer roller 46 to which a positive secondary transfer bias is applied. It is caught in the nip.

  Here, in the present copying machine, a secondary transfer nip is formed in the preceding transfer section by contact between the first intermediate transfer belt 21 that carries the first toner image and the transfer roller 46 that does not carry the toner image. . The second intermediate transfer belt 31 serving as the second toner image carrier is disposed at a position away from the preceding transfer portion. For this reason, the first toner image on the surface of the first intermediate transfer belt 21 is brought into contact with the first surface (the surface facing upward in the drawing) of the transfer paper P sandwiched between the secondary transfer nips. The second toner image on the second intermediate transfer belt 31 is not brought into contact with the surface facing downward in the drawing. In the pre-stage transfer unit, the first toner image on the first intermediate transfer belt 21 is transferred to the first surface while the transfer sheet P that is a conductive member is brought into contact with the transfer sheet P and pressed against the first intermediate transfer belt 21. Thus, a double-sided transfer device serving as a double-sided transfer means is configured so as to transfer to the surface.

  With this configuration, the second intermediate transfer belt 31 is not interposed between the first intermediate transfer belt 21 and the transfer roller 46 in which the transfer paper P is sandwiched in the upstream transfer unit. For this reason, the transfer current varies in the paper surface direction between the first intermediate transfer belt 21 and the transfer roller 46 due to the difference in density of the second toner image carried on the second intermediate transfer belt 31 and the presence of image portions. To avoid such a situation. As a result, transfer failure of the first toner image in the front transfer portion can be suppressed.

  Next, a copying machine according to a second embodiment to which the present invention is applied will be described. Note that the configuration of the copier according to the second embodiment is the same as that of the copier according to the first embodiment unless otherwise specified.

  FIG. 8 is a schematic configuration diagram showing a main configuration of the copying machine. This copying machine is different from the copying machine according to the first embodiment in the following points. That is, in the copier according to the first embodiment, the first process units 80Y, 80M, 80C, 80K, and 80K for exclusively forming only the first toner image out of the first toner image and the second toner image; And a second process unit (81Y, M, C, K) for exclusively forming the second toner image. On the other hand, the copying machine according to the second embodiment has only four first process units 80Y, 80M, 80C, 80K as process units. These first process units 80Y, 80M, 80C, 80K, and 80K form a first toner image and a second toner image on the first intermediate transfer belt 21 as a first toner image carrier. Further, in the present copying machine, a secondary transfer nip is formed by the contact between the first intermediate transfer belt 21 and the second intermediate transfer belt 31 in the front transfer unit. Therefore, the second intermediate transfer belt 31 as the second toner image carrier is brought into contact with the second surface of the transfer paper P in the front transfer portion. In the figure, the illustration of the image reading device (scanner) is omitted for convenience.

  In this copying machine, first, the first single color toner image to be transferred to the second surface of the transfer paper P is transferred to the first surface of the transfer paper P by each of the first process units 80Y, 80M, 80C, 80K. For this purpose, the first monochrome toner image is formed before the toner image. Then, each of them is transferred onto the first intermediate transfer belt 21 in a superimposed manner. Thus, a second multicolor toner image is first formed on the first intermediate transfer belt 21. The second multicolor toner image is secondarily transferred onto the second intermediate transfer belt 31 at a secondary transfer nip where the first intermediate transfer belt 21 and the second intermediate transfer belt 31 are in contact with each other.

  Each of the first process units 80Y, 80M, 80C, 80K forms a first single color toner image for a while, and then forms a second single color toner image and superimposes it on the first intermediate transfer belt 21. Transcript. Thereafter, the transfer paper P is fed into the secondary transfer nip. Then, at the secondary transfer nip, the first multicolor toner image on the first intermediate transfer belt 21 is in close contact with the first surface of the transfer paper P and is collectively secondary transferred. Next, when the transfer paper P passes through the secondary transfer nip and is conveyed to a position facing the transfer charger 47, the second multicolor toner image on the second intermediate transfer belt 31 is formed on the second surface of the transfer paper P. Batch transfer is performed.

  In the copying machine configured as described above, a first image forming unit including a first process unit dedicated for forming a first toner image, a second process unit dedicated for forming a second toner image, and the like. A toner image can be formed on each side of the transfer paper by the one-pass method without providing both of the second image forming unit. However, since it is necessary to form the first toner image and the second toner image at different times, compared with the copying machine according to the first embodiment that can form both toner images in parallel, The image forming speed is reduced. On the other hand, in the copying machine according to the first embodiment, by providing both the first image forming unit and the second image forming unit, it is possible to increase the image forming speed instead of increasing the cost.

  As in the present copying machine, the first intermediate transfer belt 21 and the like on the second surface while the first toner image carrier such as the first intermediate transfer belt 21 and the like are in contact with the first surface of the transfer paper P in the front transfer unit. In the case where the second toner image carrier is brought into contact, the first toner image tends to be poorly transferred. This is because the transfer current greatly varies in the paper surface direction when the difference in density of the second toner image carried on the second toner image carrier is large, or when the degree of dot distribution of the image portion is large.

  FIG. 9 shows a second toner image (other color second toner image) of the front transfer portion in the case where an image portion having a greater degree of dot distribution than the first toner image (multicolor first toner image) is formed. It is an expansion schematic diagram which shows a state. In the figure, the transfer current is transferred from the transfer counter roller 28 via the first intermediate transfer belt 21, the first toner image p 1, the transfer paper P, the second toner image p 2, and the second intermediate transfer belt 31. Then, it flows into the transfer roller 46. Between the first intermediate transfer belt 21 and the first surface of the transfer paper P, or between the second surface of the transfer paper P and the second intermediate transfer belt 31, at a place where there is little toner having a very large electric resistance. The transfer current flows mainly. Then, the variation in the paper surface direction of the transfer current between the first intermediate transfer belt 21 and the first surface of the transfer paper P is the first sandwiched between the second surface of the transfer paper P and the second intermediate transfer belt 31. It depends on the density difference in the paper surface direction of the two toner images p2 and the degree of image portion dot distribution. When the density difference in the paper surface direction of the second toner image p2 and the degree of image portion doting are large, as shown in the figure, the transfer current from the first intermediate transfer belt 21 mainly causes the toner presence location ( Or, it flows toward a place where the toner amount is small. For this reason, in the first toner image p1, the transfer current flowing in the portion of the second surface facing the toner existing location (or the location where the amount of toner is large) is insufficient, causing a transfer failure.

  FIG. 10 is an enlarged schematic diagram showing the state of the pre-transfer portion when a second toner image having an image portion with a smaller degree of dot distribution than the first toner image is formed. In the drawing, the second toner image p2 is sandwiched between the second surface of the transfer paper P and the second intermediate transfer belt 31 with a substantially uniform thickness in the paper surface direction. Then, the transfer current from the first intermediate transfer belt 21 flows almost uniformly in the paper surface direction between the first intermediate transfer belt 21 and the first surface of the transfer paper P, so the first toner image p1. Transfer defects can be suppressed.

  Therefore, in this copying machine, the toner image is formed as follows in accordance with image information sent from an image reading device or a personal computer not shown in FIG. Forming means. That is, if necessary, the relationship between the first toner image and the second toner image is reversed to form the first toner image as the second toner image and the second toner image as the first toner image. is there. More specifically, when it is determined based on the image information that the second toner image has a greater density difference in the paper surface direction or a degree of image portion doting than the first toner image, the first toner image and the second toner image It reverses the relationship with the image. As a result, the toner image represented as the first toner image in the image information is formed as the second toner image, and in the former transfer portion, between the second surface of the transfer paper P and the second intermediate transfer belt 31. It is caught. Then, when the toner image is formed according to the image information, the state as shown in FIG. 9 is caused and the transfer of the toner image on the first surface is caused. Thus, transfer failure of the toner image on the first surface can be suppressed.

This copier specifies to the user that Y, M, C, and K toners used to form a toner image should satisfy the following conditions (a) to (d). ing.
(A) The weight average particle diameter is 3 to 8 [μm].
(B) A value obtained by dividing the weight average particle diameter D4 by the number average particle diameter D1 is 1.00 to 1.40.
(C) The average circularity is 0.93 to 1.00.
(D) Silica fine particles having an average particle diameter of 50 to 300 [nm] and a bulk density of 0.3 [g / cm ³ ] or more are held on the surface (externally added).

  As a method for instructing the user to use such toner, for example, a toner having all of the above conditions (a) to (e) can be packed and shipped together with a printer. Further, for example, the product number or product name of the toner may be specified in the printer main body or the instruction manual. Further, for example, it may be performed by notifying the user of the product number, product name, etc. in writing or electronic data. Further, for example, it can be performed by shipping a toner bottle, which is a toner storing means for storing such toner, set in the printer main body. This printer employs all these methods, but it is sufficient to employ at least one of the methods.

  The reason why the toner satisfying the condition (a) is designated is as follows. In other words, when the toner has a weight average particle size smaller than 3 [μm], when used as a two-component developer, the toner fuses to the surface of the carrier during long-term agitation in the developing device, thereby reducing the charging ability of the carrier Because. When used as a one-component developer, toner filming on the developing roller and toner fusion to a member such as a blade for thinning the toner are likely to occur. Conversely, when the weight average particle size is larger than 0.99, it becomes difficult to obtain a high-resolution and high-quality image, and when the balance of the toner in the developer is performed, the particle size of the toner This is because fluctuations often increase.

In the case of reproducing minute dots having a resolution of 600 dpi or more, the characteristic of a weight average particle diameter of 3 to 8 μm is particularly effective. In this range, since the toner particles have a sufficiently small particle size with respect to the minute latent image dots, the dot reproducibility is excellent.
When the weight average particle diameter is less than 3 μm, phenomena such as a decrease in transfer efficiency and a decrease in blade cleaning properties tend to occur. Further, if the weight average particle size (D4) exceeds 8 μm, it is difficult to suppress scattering of characters and lines.

  The reason why the toner satisfying the condition (b) is specified is as follows. That is, when the value obtained by dividing the weight average particle diameter by the number average particle diameter is in the range of 1.00 to 1.40, various merits are generated. For example, a phenomenon in which toner particles having a particle size suitable for an electrostatic latent image pattern contributes to development preferentially over other toners, so that various patterns of images can be stably formed. There is a merit that it becomes possible to do. In addition, when the apparatus adopts a configuration in which toner remaining on an image carrier such as a photoreceptor is collected and recycled, a large amount of small-size toner particles that are difficult to be transferred are recycled. In such recycling, when the above-mentioned one having a relatively large value is used, the development performance is adversely affected due to a large change in the toner particle size from the new toner supply to the next toner supply.

  The weight average particle diameter and number average particle diameter of the toner can be measured by a measuring device using a Coulter counter method, for example, Coulter Counter TA-II or Coulter Multisizer II (both manufactured by Coulter). Specifically, 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. As the electrolytic aqueous solution, approximately 1% NaCl aqueous solution is prepared using primary sodium chloride, and for example, ISOTON-II (manufactured by Coulter) can be used. Further, 2 to 20 mg of a measurement sample is added to the obtained solution. Then, the solution is dispersed for about 1 to 3 minutes with an ultrasonic disperser, and the weight and number of toners are measured by the above-described measuring apparatus using a 100 μm aperture as an aperture to calculate the weight distribution and the number distribution. To do. From the obtained distribution, the weight average particle diameter and the number average particle diameter of the toner can be obtained. In addition, as a channel, it is less than 2.00-2.52 micrometer; 2.52-3.17 micrometer; 3.17-4.00 micrometer; 4.00-5.04 micrometer; 5.04-6.35 micrometer 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; Intended for toner particles having a particle size of 2.00 μm to less than 40.30 μm using 13 channels of less than 25.40 μm; 25.40 to less than 32.00 μm; 32.00 to less than 40.30 μm.

  The reason why the toner satisfying the condition (c) is specified is as follows. That is, when the average circularity of the toner is less than 0.93, that is, when the shape of the toner starts to be indefinite rather than spherical, the transferability starts to deteriorate rapidly, and the transfer dust at the time of electrostatic transfer rapidly increases. This is because it is easy to occur. Furthermore, if the average circularity is less than 0.93, it becomes difficult to form a high-definition image having a reproducibility with an appropriate density. When the average circularity is in the range of 0.90 to 1.00, the surface of the toner particles is smooth, and the toner particles and the contact area between the toner particles and the photosensitive member are small, so that the transferability is excellent. Since the toner particles have no corners, the developer agitation torque in the developing device is small, and the agitation drive is stabilized, so that no abnormal image is generated. In addition, since there are no angular toner particles in the toner forming the dots, when the pressure is brought into contact with the transfer medium during transfer, the pressure is uniformly applied to the entire toner forming the dots, and the transfer is not easily lost. In addition, since the toner particles are not angular, the abrasive power of the toner particles themselves is small, and the surface of the photoreceptor, the charging member, etc. is not damaged or worn. A more preferable range of the average circularity is 0.93 to 0.97, and it is more preferable that the toner particles having a circularity of less than 0.94 are limited to 10% or less.

  The average circularity of the toner can be measured as follows. That is, first, a suspension containing toner particles of the toner to be tested is passed through an imaging unit detection zone on a flat plate, and the particle image is optically captured by a CCD camera. Then, for each particle image, an average value of the values obtained by dividing the perimeter of an equivalent circle having the same projected area by the perimeter of the actual particle is calculated. This average value is the average circularity. In order to measure the average circularity, for example, a flow type particle image analyzer FPIA-2100 (manufactured by Toa Medical Electronics Co., Ltd.) may be used. In the case of using this apparatus, 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. Further, about 0.1 to 0.5 [g] of the test toner is added. Then, this suspension was subjected to dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes, and the dispersion concentration was adjusted to 3000 to 1 [10,000 / μl], and the shape and distribution of the toner were measured using the above apparatus. To do.

The reason why the toner satisfying the condition (d) is specified is as follows. That is, when silica fine particles having an average particle size of 50 to 300 [nm] and a bulk density of 0.3 [g / cm ³ ] or more are externally added to the toner base resin, the toner from the transfer source such as a transfer belt is transferred. This is because the releasability is rapidly improved and excellent transferability can be exhibited.

Next, a description will be given of each example of a copying machine in which a more characteristic configuration is added to the copying machine according to the second embodiment.
[First embodiment]
In the copying machine according to the first embodiment, the toner image forming means is configured as follows. That is, the image area ratio of the first toner image and the image area ratio of the second toner image are calculated by a well-known technique based on image information sent from the image reading apparatus or the personal computer. The image area ratio is the ratio of toner-attached pixels to which toner is attached in all the pixels in the area where an image can be formed on the photoreceptor. A toner image having a large image area ratio is more likely to have a greater degree of dot distribution in an image portion (a portion to which toner is attached on the paper surface) than a toner image having a small image area ratio. Therefore, when the image area ratio of the second toner image calculated based on the image information is smaller than the image area ratio of the first toner image, the relationship between the first toner image and the second toner image is reversed. Each toner image is formed.

[Second Embodiment]
In the copying machine according to the first embodiment, the toner image forming means is configured as follows. That is, the image area ratio of the first toner image and the image area ratio of the second toner image are calculated by a well-known technique based on image information sent from the image reading apparatus or the personal computer. The image area ratio is the ratio of toner-attached pixels to which toner is attached in all the pixels in the area where an image can be formed on the photoreceptor. A toner image with a small image area ratio is more likely to have a greater degree of dot distribution in an image portion (a portion to which toner is attached on the paper surface) than a toner image with a large image area ratio. Therefore, when the image area ratio of the second toner image calculated based on the image information is smaller than the image area ratio of the first toner image, the relationship between the first toner image and the second toner image is reversed. Each toner image is formed.

  The inventor conducted the following experiment. That is, first, image information in which the image area ratio of the first toner image is 90 [%] and the image area ratio of the second toner image is 60 [%] is sent to the copier, and each toner image is sent. Was formed as it was. As a result, a partial transfer failure occurred in the first toner image. Next, the same image information was sent, and both toner images were formed by reversing the relationship between the first toner image and the second toner image. Then, the toner image formed on the first surface of the transfer paper P (which is represented as the second toner image in the image information) has a stable quality without causing transfer failure. Therefore, based on the image area ratio, the relationship between the first toner image and the second toner image is reversed as necessary to form the respective toner images, so that transfer defects on the first surface can be improved. Experiments have confirmed that it can be suppressed.

In the above-described experiment, the first intermediate transfer belt 21 has a surface resistance of 1.0 × 10 ¹¹ [Ω / □] and a volume resistivity of 5.0 × 10 ⁸ [Ω · cm]. Using. Further, as the second intermediate transfer belt 31, a belt having a surface resistance of 1.0 × 10 ⁹ [Ω / □] and a volume resistivity of 1.0 × 10 ⁷ [Ω · cm] was used. Further, the transfer roller 46 having a volume resistivity of 1.0 × 10 ⁷ [Ω · cm] was used. Further, the transfer current in the front transfer portion was maintained at 20 [μA] by constant current control. Further, the transfer nip pressure at the front transfer portion was set to 230 [g / cm ² ]. The transfer current by the transfer charger 47 was set to 230 [μA].

[Second Embodiment]
In the copying machine according to the second embodiment, the toner image forming means is configured as follows. That is, based on image information sent from an image reading device or a personal computer, the average image density of the first toner image and the average image density of the second toner image are calculated by a known technique. With respect to this average image density, in the case where halftone is expressed by dithering, the ratio of the toner adhering pixels in all the pixels in the area where the image can be formed on the photoconductor is obtained for each color, and the average is calculated. Can be determined by Further, in the case of expressing a halftone by changing the toner adhesion amount with respect to each toner adhesion pixel, it can be obtained based on the accumulation of the toner adhesion amount of each toner adhesion pixel. A toner image with a low average image density is more likely to have a greater density difference in a halftone portion than a toner image with a high average image density. Therefore, when the average image density of the second toner image calculated based on the image information is lower than the average image density of the first toner image, the relationship between the first toner image and the second toner image is reversed. Each toner image is formed.

[Third embodiment]
In the copier according to the third embodiment, the toner image forming means is configured as follows. That is, based on image information sent from the image reading apparatus or personal computer, the difference between the maximum image density and the minimum image density (minimum image density in the halftone portion) of the first toner image, and the second toner image The difference between the maximum image density and the large and small image density is calculated by a known technique. A toner image having a large difference between the maximum image density and the minimum image density is more likely to have a greater density difference than a toner image having a small difference. Therefore, when the difference between the second toner images calculated based on the image information is larger than that of the first toner image, the relationship between the first toner image and the second toner image is reversed, and the respective toner images are reversed. Form.

[Fourth embodiment]
The copier according to the fourth embodiment includes a reversing unit shown in FIG. 11 on the side of the fixing device 60 shown in FIG. In the figure, the transfer paper P (not shown) is delivered from the fixing device 60 to the reversing unit in a posture extending substantially horizontally. The reversing unit, which is a reversing unit, accepts the transfer paper sent from the fixing device 60 in the first conveyance path C1 in its posture. In the vicinity of the end of the first transport path C1, a switching claw 61 is disposed so as to be rotatable about a rotation shaft 61a. When the switching claw 61 stops rotating in a posture that causes the main body to extend substantially horizontally as shown in the drawing, the transfer paper is switched while maintaining the posture immediately after being fed from the fixing device 60. It passes through the upper surface of the claw 61 and reaches the second transport path C2. Then, the sheet is discharged from the second conveyance path C2 to the outside of the apparatus through a pair of discharge rollers (not shown). That is, when the switching claw 61 is in the state shown in the drawing, the transfer sheet sent out from the fixing device 60 is discharged outside the apparatus while maintaining the posture immediately after the sending out.

  On the other hand, when the rotation of the switching claw 61 is stopped at a predetermined angle counterclockwise around the rotation shaft 61a, the transfer paper sent from the fixing device 60 is transferred to the first transport path C1. After being received, the contact with the switching claw 61a is made and the tip thereof is directed downward in the figure. Then, after entering the third conveyance path C3 and being sent from the upper side to the lower side in the figure, this time, the tip is directed rightward in the figure and enters the fourth conveyance path C4. Further, the sheet is fed from the left side to the right side in the figure in the fourth conveyance path C4. When almost the entire transfer paper enters the fourth transport path C4 by this transport, the transport roller pair provided at the entrance of the fourth transport path C4 starts to rotate in the opposite direction. Then, this time, the transfer sheet is sent from the right side to the left side in the drawing with the rear end at the top, and enters the fifth transport path C5. Then, the paper is sent from the lower side to the upper side in the drawing in the fifth transport path C5, and reaches a pair of paper discharge rollers (not shown). At this time, the transfer paper is in a posture that is reversed from the state immediately after being sent from the fixing device 60. In this way, the reversing unit shown in the drawing reverses the transfer paper sent out from the fixing device 60 as necessary, and sends it to a pair of paper discharge rollers (not shown).

  Based on the image information, if both toner images are formed by reversing the relationship between the first toner image and the second toner image as necessary, the second toner image that was originally supposed to be transferred to the first surface is transferred to the second image. The toner image that should have been transferred to the second surface is transferred to the first surface. Then, the state of the transfer paper after the printout is reversed from the original one. Therefore, in this copying machine, when the reversing unit shown in the figure is provided and both the toner images are formed by reversing the relationship between the first toner image and the second toner image, the transfer paper is reversed. It is designed to discharge afterwards. Further, when both toner images are formed without reversing the same relationship, the transfer paper is discharged without being reversed. Whether or not the front and back are reversed is determined by a switching claw 61 serving as a conveyance path switching means for switching the conveyance path of the recording medium between a path (C3 to C5) for reversing the transfer paper and a path (C2) for not reversing the front and back. In such a configuration that can be selected, even if both the toner images are formed with the relationship between the first toner image and the second toner image reversed or not formed, they are discharged out of the apparatus. The relationship between the upper surface and the lower surface of the transfer paper can be aligned with the original relationship.

[Fifth embodiment]
The copier according to the fifth embodiment, like the copier according to the first embodiment, reverses the relationship between the first toner image and the second toner image as necessary based on the image area ratio. Both toner images are formed.
FIG. 12 is an enlarged configuration diagram showing a front transfer unit of the copying machine. In the experiment described previously in the first embodiment, a solid image having an image area ratio of 60% shown in FIG. 13 is formed on the first surface of the transfer paper in the secondary transfer nip shown in FIG. Transferred onto the belt 21. At this time, in the secondary transfer nip, a solid image having an image area ratio of 90% shown in FIG. 14 is interposed as the second toner image between the second surface of the transfer paper and the second intermediate transfer belt 31. It was. Comparing FIG. 13 and FIG. 14, an image portion to which toner adheres is formed on the entire surface of the transfer paper. The density of each dot in the image portion is only lower in FIG. 15 than in FIG.

  FIG. 15 is a schematic diagram showing the entire surface solid toner image pi having an image area ratio of about 95% together with the transfer paper P. FIG. 16 is a schematic diagram showing, together with the transfer paper P, five patch solid toner images pi in which the toner adhesion amount per unit area is the same as that of the entire solid toner image of FIG. The transfer paper P in FIG. 16 does not have a solid toner image formed on the entire surface thereof, but is in a state where patch solid toner images pi are scattered in places. In such a case, there is a very large difference in toner amount between the patch solid toner image pi and the non-image portion. Therefore, the variation in the paper direction of the transfer current when the batch shown in FIG. 16 is formed as the second toner image is the paper direction of the transfer current when the toner image shown in FIG. 13 is formed as the second toner image. It will be much larger than the variation.

  The patch toner image shown in FIG. 16 and the full solid toner image shown in FIG. 15 are reversed from the relationship between the second toner image and the first toner image to the relationship between the first toner image and the second toner image. In this case, it was possible to suppress the transfer failure on the first surface rather than the reverse rotation. However, a transfer defect that was still visible was still confirmed.

  Therefore, in this copying machine, when the image area ratio of one toner image and the image area ratio of the other toner image exceed a predetermined threshold, the transfer current is changed from the standard value. Thus, it is configured to exhibit better transferability. The transfer current is changed by changing the current target value in the known constant current control. With the copying machine configured as described above, the patch shown in FIG. 16 is formed as the first toner image, while the entire solid toner image shown in FIG. 15 is formed as the second toner image. The transfer failure of the first toner image on the top is greatly improved.

[Sixth embodiment]
In the copier according to the sixth embodiment, when the image area ratio of one toner image and the image area ratio of the other toner image have a difference equal to or larger than a threshold, as in the copier according to the fifth embodiment. In addition, the transfer conditions in the previous transfer section are changed. However, not the transfer current but the nip pressure (transfer pressure) is changed as the transfer condition. As a method of changing the nip pressure, the method shown in FIG. 17 is adopted. That is, in the configuration in which the circumferential surface of the eccentric cam 62 is abutted against the shaft member 46 a of the transfer roller 46 and the transfer roller 46 is biased toward the transfer counter roller 28, the biasing force by the cam is caused by the eccentric rotation of the eccentric cam 62. By changing the nip pressure, the nip pressure is changed. Instead of such a configuration, as shown in FIG. 18, the contact pressure between the transfer facing roller 28 and the transfer roller 46 is changed by moving the second transfer unit (30) up and down together with the support member that supports the second transfer unit (30). You may do it. As a method of moving the support body up and down, as shown in the figure, in addition to a method in which the eccentric cam 62 is abutted against the support body, a moving system using a solenoid or the like may be employed.

In this way, by changing the nip pressure as necessary, the first surface is solid and the second surface is patched (the relationship in image information is opposite to this), as in the copying machine according to the fifth embodiment. ), The solid transfer failure of the first surface could be effectively suppressed.
Note that the mechanism for moving the transfer roller 46 and the support up and down in FIG. 17 functions as a contact pressure changing unit that changes the contact pressure between the surface of the toner image carrier and the first surface in contact with the toner image carrier in the front transfer unit. Yes.

[Example 7]
Similarly to the copier according to the fifth embodiment, the copier according to the seventh embodiment also has a difference between the image area ratio of one toner image and the image area ratio of the other toner image that is equal to or greater than a threshold value. In addition, the transfer conditions in the previous transfer section are changed. However, as a transfer condition, not the transfer current or the nip pressure but the nip width is changed. The nip width is the length of the nip (secondary transfer nip in this example) in the recording material conveyance direction. As a method for changing the nip width, the method shown in FIG. 19 is adopted. That is, on the inner side of the loop of the second intermediate transfer belt, the nip downstream roller 48 adjacent to the transfer roller 46 on the downstream side in the movement direction of the second intermediate transfer belt 31 is provided and moved up and down. When the nip downstream roller 48 moves upward in the drawing, the amount of winding of the second intermediate transfer belt 31 around the transfer counter roller 28 becomes larger, and the nip width becomes larger. On the contrary, when the nip downstream roller 48 moves downward in the figure, the winding amount of the second intermediate transfer belt 31 around the transfer counter roller 28 becomes smaller and the nip width becomes smaller.

  As a method of changing the nip width, as shown in FIG. 20, instead of the nip downstream roller shown in FIG. 19, a nip upstream roller 49 adjacent to the transfer roller 46 in the vicinity of the upstream side in the belt moving direction is provided. This may be moved up and down. Further, as shown in FIG. 21, the transfer roller 46 is arranged so as to be shifted from the position where it contacts the transfer counter roller 28 via the belt, and the nip upstream roller 49 is moved up and down while moving the roller up and down. It may be adopted.

As described above, by changing the nip width as necessary, the first surface is solid and the second surface is a patch (the relationship in image information is the same as in the copier according to the fifth embodiment). Even in the case of forming each of the reverse), the solid transfer failure of the first surface could be effectively suppressed.
The mechanism for moving the roller up and down shown in FIGS. 19 to 21 functions as a contact area changing means for changing the contact area between the surface of the toner image carrier and the first surface in contact with the surface of the toner image carrier in the front transfer unit. Yes.

  So far, examples of using a drum-shaped photoconductor as a latent image carrier have been described. However, other types such as a belt-shaped photoconductor may be used. Further, although an example of forming a full-color image has been described, an image forming apparatus that forms a single-color image using one photoconductor (image carrier) may be used. Further, the copying machine for transferring the toner image from the intermediate transfer belt as the toner image carrier onto the transfer paper P has been described. However, the toner image is transferred onto the transfer paper P from a latent image carrier such as a photoreceptor as the toner image carrier. The present invention can also be applied to the image forming apparatus. Further, although a copying machine that forms an image by an electrophotographic method has been described, the present invention can also be applied to an image forming apparatus that forms a toner image by other methods such as a direct recording method. This direct recording method is not related to a latent image carrier, but forms a dot image by directly adhering a toner group that has been ejected in a dot shape from a toner flying device to a recording medium or an intermediate recording medium. In this method, a toner image is directly formed on an intermediate recording medium. In the configuration in which the toner image is transferred from the intermediate recording medium to a recording medium such as transfer paper after the toner is ejected from the toner flying device toward the intermediate recording medium, the recording medium is similar to the electrophotographic system. The roughness of the image differs depending on the surface smoothness.

  As described above, in the copier according to the third embodiment, the relationship between the first toner image and the second toner image is reversed according to the difference between the maximum image density and the minimum image density of the toner image calculated based on the image information. Thus, a toner image forming unit including each first process unit, the control unit 95, and the like is configured so as to form each toner image. In this configuration, as described above, the relationship between the first toner image and the second toner image can be reversed in accordance with the difference so as to suppress variations in the transfer current in the paper surface direction in the preceding transfer unit. .

  In the copier according to the first embodiment, the relationship between the first toner image and the second toner image is reversed according to the image area ratio of the toner image calculated based on the image information, and each toner image is displayed. A toner image forming unit is configured to form the toner image. In such a configuration, as described above, the relationship between the first toner image and the second toner image can be reversed in accordance with the image area ratio so as to suppress variations in the transfer current in the paper surface direction in the front transfer unit. it can.

  In the copying machine according to the second embodiment, the relationship between the first toner image and the second toner image is reversed according to the average image density of the toner image calculated based on the image information, and the respective toner images are displayed. A toner image forming unit is configured to form the toner image. In this configuration, as described above, the relationship between the first toner image and the second toner image can be reversed in accordance with the average image density so as to suppress variations in the transfer current in the paper surface direction in the preceding transfer unit. it can.

  Further, in the copying machine according to the fourth embodiment, a reversing unit as a reversing unit for reversing the front and back of the transfer paper after passing through the fixing device 60 as a fixing unit is provided. Further, the reversing unit is provided with a switching claw 61 serving as a conveyance path switching means for switching the conveyance path of the transfer paper P after passing through the fixing device 60 fixing means between a reverse-inverted path and a non-inverted path. In such a configuration, as described above, even if both the toner images are formed with the relationship between the first toner image and the second toner image reversed or not, the transfer is discharged out of the apparatus. The relationship between the upper and lower surfaces of the paper can be aligned with the original relationship.

  In the copying machine according to the fifth embodiment, a double-sided transfer unit including a first transfer unit, a second transfer unit, a transfer bias power source, and the like is configured to change a transfer current according to image information. . In such a configuration, as described above, even when a toner image that greatly varies the transfer current in the paper surface direction is formed like a patch image, transfer defects on the first surface can be effectively suppressed.

  Further, in the copying machine according to the sixth embodiment, the contact pressure that changes the contact pressure between the surface of the first intermediate transfer belt 21 and the first surface of the transfer paper in contact with the surface in the front transfer unit according to the image information. Since the changing means is provided, for the reason described above, even when a toner image that greatly increases the variation in the paper current direction of the transfer current is formed like a patch image, transfer defects on the first surface are effectively suppressed. Can do.

  Further, in the copier according to the seventh embodiment, the contact area for changing the contact area between the surface of the first intermediate transfer belt 21 and the first surface of the transfer paper in contact with the surface in the front transfer unit according to the image information. Since the changing means is provided, for the reason described above, even when a toner image that greatly increases the variation in the paper current direction of the transfer current is formed like a patch image, transfer defects on the first surface are effectively suppressed. Can do.

  In the copying machines according to the fifth, sixth, and seventh embodiments, if at least two of the transfer current, the nip pressure, and the nip width are changed independently of each other, the transfer defect on the first surface is further increased. It can be suppressed well.

FIG. 3 is an enlarged schematic diagram illustrating an example of a configuration of a front transfer unit. FIG. 6 is an enlarged schematic diagram illustrating a front transfer portion when a second toner image having a solid shape without dot portions is formed. FIG. 4 is an enlarged schematic diagram illustrating a front transfer portion when a second toner image p2 in which image portions are scattered is formed. 1 is a schematic configuration diagram showing a copier according to a first embodiment. FIG. 2 is an enlarged configuration diagram showing a first process unit of the copier. FIG. 3 is an enlarged configuration diagram showing a second process unit of the copier. FIG. 2 is an enlarged configuration diagram illustrating an enlarged front transfer unit and a rear transfer unit of the copier. FIG. 9 is a schematic configuration diagram illustrating a main configuration of a copying machine according to a second embodiment. FIG. 3 is an enlarged schematic diagram illustrating a state of a front transfer unit of the copier when a second toner image having an image portion with a greater degree of dot distribution than the first toner image is formed. FIG. 3 is an enlarged schematic diagram illustrating a state of a front transfer unit of the copier when a second toner image having an image portion with a dot density smaller than that of the first toner image is formed. FIG. 10 is a schematic configuration diagram illustrating a reversing unit of a copying machine according to a fourth embodiment. FIG. 10 is an enlarged configuration diagram illustrating a front transfer unit of a copying machine according to a fifth embodiment. FIG. 3 is a schematic diagram showing a transfer paper on which a full-color image with an image area ratio of 60% is formed. FIG. 3 is a schematic diagram illustrating a transfer sheet on which a full-color image having an image area ratio of 90% is formed. FIG. 3 is a schematic diagram showing a transfer paper on which a full-color image having an image area ratio of 95% is formed. FIG. 6 is a schematic diagram illustrating a transfer sheet on which five patch solid images are formed. The expanded block diagram which shows the front | former stage transfer part of the copying machine based on 6th Example. FIG. 6 is a configuration diagram showing a modification of the double-sided transfer device of the copier. The expanded block diagram which shows the front | former stage transfer part of the copying machine based on 7th Example. FIG. 3 is an enlarged configuration diagram illustrating a first modification of a front transfer unit of the copier. FIG. 3 is an enlarged configuration diagram illustrating a first modification of a front transfer unit of the copier.

Explanation of symbols

P Transfer paper (recording medium)
1Y, M, C, K photoconductor (latent image carrier)
5 Development device (developing means)
20 First transfer unit (part of transfer means)
21 First intermediate transfer belt (first toner image carrier)
30 Second transfer unit (part of transfer means)
46 Conductive member 80Y, M, C, K First process unit (part of toner image forming means)
81Y, M, C, K Second process unit (part of toner image forming means)
95 Control part (part of toner image forming means)

Claims (13)

A first toner image recorded on the first surface of the recording medium is formed on the first toner image carrier, and a second toner image recorded on the second surface of the recording medium is formed on the second toner image carrier. Toner image forming means,
A transfer current is generated between the first toner image carrier and the first surface at a pre-transfer portion where the first toner image carrier and the first surface are brought into contact with each other. After the toner is transferred to the first surface, the second toner image carrier and the second surface are brought into contact with each other at a subsequent transfer portion where the charge applying unit is opposed to the first surface through a predetermined gap. A transfer unit that applies a charge to the first surface by the charge applying unit and transfers the second toner image to the second surface;
Fixing means for fixing toner images on both sides of the recording medium after passing through the transfer means,
In an image forming apparatus that forms images on both sides of the recording medium by a one-pass method,
The second toner image carrier is disposed at a position away from the front transfer unit, and a conductive member that contacts the first toner image carrier is provided in the front transfer unit. The recording body is sandwiched between the first toner image carrier and the conductive member, and the conductive member presses the recording body from the second surface side toward the first toner image carrier. However, an image forming apparatus comprising the transfer unit configured to transfer the first toner image on the first toner image carrier onto the first surface. Based on the image information, the first toner image recorded on the first surface of the recording member and the second toner image recorded on the second surface of the recording member are formed on the same toner image carrier, or Toner image forming means for forming individual toner images on different toner image carriers; and
A transfer current is generated between the surface of the toner image carrier and the first surface at a pre-transfer portion where the surface of the toner image carrier on which the first toner image is formed and the first surface are brought into contact with each other. Then, after transferring the first toner image from the surface of the toner image carrier to the first surface, the second transfer unit that makes the charge applying unit face the first surface with a predetermined gap therebetween. A transfer unit configured to transfer the second toner image to the second surface by applying a charge to the first surface by the charge applying unit while bringing the toner image carrier into contact with the second surface;
Fixing means for fixing toner images on both sides of the recording medium after passing through the transfer means,
In an image forming apparatus that forms images on both sides of the recording medium by a one-pass method,
According to the image information, the relationship between the first toner image and the second toner image is reversed to form the first toner image as the second toner image and the second toner image as the first toner image. An image forming apparatus comprising the toner image forming means. The image forming apparatus according to claim 2.
The relationship between the first toner image and the second toner image according to the difference between the maximum image density and the minimum image density of the toner image included in the image information or calculated based on the image information. An image forming apparatus characterized in that the toner image forming means is configured so as to form respective toner images by reversing each other. The image forming apparatus according to claim 2.
In accordance with the image area ratio information of the toner image that is included in the image information or calculated based on the image information, the relationship between the first toner image and the second toner image is reversed to An image forming apparatus comprising the toner image forming unit configured to form a toner image. The image forming apparatus according to claim 2.
According to the average image density of the toner image included in the image information or calculated based on the image information, the relationship between the first toner image and the second toner image is reversed, and each toner is An image forming apparatus comprising the toner image forming unit configured to form an image. The image forming apparatus according to any one of claims 2 to 5,
Reversing means for reversing the front and back of the recording body after passing through the fixing means;
An image forming apparatus, comprising: a conveyance path switching unit that switches a conveyance path of the recording material after passing through a fixing unit between a path that reverses the front and back and a path that is not reversed. The image forming apparatus according to any one of claims 2 to 6,
An image forming apparatus, wherein the transfer unit is configured to change the transfer current in accordance with the image information. The image forming apparatus according to any one of claims 2 to 7,
According to the image information, the transfer means is provided with contact pressure changing means for changing the contact pressure between the surface of the toner image carrier and the first surface in contact with the surface of the toner image carrier in the front transfer portion. Image forming apparatus. The image forming apparatus according to claim 8.
An image forming apparatus using the contact pressure changing means that changes the contact pressure using rotation of an eccentric cam. The image forming apparatus according to any one of claims 2 to 7,
According to the image information, the transfer means is provided with contact area changing means for changing the contact area between the surface of the toner image carrier and the first surface in contact with the surface of the toner image carrier in the front transfer portion. Image forming apparatus. The image forming apparatus according to claim 10.
As the toner image carrier, a toner carrying belt that is moved endlessly while being stretched by a plurality of tension members,
An image forming apparatus using the contact area changing means that changes the contact area by moving the tension member and changing the tension posture of the toner carrying belt. The image forming apparatus according to any one of claims 7 to 11,
An image forming apparatus, wherein at least two of the transfer current, contact pressure and contact area are changed independently of each other. The image forming apparatus according to claim 1,
A toner containing means for containing toner used in the toner image forming means;
A toner having a weight average particle diameter of 3 to 8 [μm] and a value obtained by dividing the weight average particle diameter by the number average particle diameter of 1.00 to 1.40 is accommodated in the toner accommodating means. An image forming apparatus.

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