JP4946259B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus using an electrophotographic system.

  Conventionally, an image forming apparatus using an electrophotographic method is known. In such an image forming apparatus, generally, an electrostatic latent image corresponding to an image formed by charging the surface of a photoreceptor with a charging device such as a charger and exposing the charged photoreceptor surface with an exposure device. And a developer containing at least a precharged toner is attached to the electrostatic latent image by electrostatic force to form a toner image corresponding to the electrostatic latent image on the photoreceptor. The toner image formed on the photoconductor is transferred to the intermediate transfer belt by an electric field formed between the photoconductor and the intermediate transfer belt, and further formed between the intermediate transfer belt and the recording medium. Transfer to a recording medium by an electric field. The toner image transferred to the recording medium is fixed by a fixing device, thereby forming an image on the recording medium.

  In such an image forming apparatus, as a method of forming a color image on a recording medium, the image forming apparatus is provided with a developing device that stores toners of four colors of YMCK (yellow, magenta, cyan, black). A method is known in which each color toner image corresponding to each color image is sequentially formed on a photoreceptor, and each color toner image is sequentially transferred onto an intermediate transfer belt and then transferred onto a recording medium. Also, in the case of forming a one-color image, such a method of forming an image on a recording medium via an intermediate transfer belt may be used.

  Various types of recording media are required for such an image forming apparatus. Examples of the recording media include a recording medium having a smooth surface and a recording medium having unevenness formed on a surface called embossed paper. In the above image forming apparatus, when an image is formed on a recording medium so-called embossed paper having irregularities on the surface, a high density region having a predetermined density or more compared to a case where an image is formed on a recording medium so-called plain paper having a flat surface. Alternatively, image quality deterioration may occur in a low density region less than a predetermined density.

  In an image forming apparatus using an electrophotographic system, each toner constituting a toner image transferred from a photosensitive member onto an intermediate transfer belt by an electrostatic force generated by a transfer electric field between the intermediate transfer belt and a recording medium is transferred to the intermediate transfer belt. The toner is transferred from the belt side to the recording medium and transferred to the recording medium. To move the toner image on the intermediate transfer belt to the recording medium side well, the toner is favorably removed according to the amount of charge of the toner. An electric field that can be moved must be formed between the intermediate transfer belt and the recording medium.

  For this reason, the toner image is transferred to the recording medium by predetermining the electric field strength corresponding to the charge amount of the toner constituting the toner image transferred onto the intermediate transfer belt.

  However, if the electric field formed between the intermediate transfer belt and the recording medium is constant regardless of the image density, when the recording medium to be image-formed is embossed paper having irregularities on the surface, for example, an intermediate As the electric field strength of the electric field formed between the transfer belt and the recording medium, if the strength for moving the toner that forms a high density region of a predetermined density or higher to the recording medium side is determined, a low density less than the predetermined density When the toner forming the area is transferred to the recording medium, an excessive electric field is generated to cause discharge in the gap between the intermediate transfer belt and the recording medium, and the toner adhering to the intermediate transfer belt is charged with a reverse polarity. As a result, there is a case where the image is not moved to the recording medium and the image quality is deteriorated.

  On the other hand, if the electric field strength for moving the toner that forms a low density region less than the predetermined density to the recording medium side is set as the strength of the electric field formed between the intermediate transfer belt and the recording medium, a high density region is formed. It may be difficult to move all of the toner to the recording medium side.

Patent Document 1 discloses a predetermined Young's modulus for the purpose of eliminating as much as possible the gap generated between the recess of the embossed paper and the surface of the intermediate transfer belt in order to obtain a good transfer without imperfect transfer with the embossed paper having irregularities. An intermediate transfer belt made of a rubber material having an elastic layer is described, and Patent Document 2 describes an intermediate transfer belt having a multilayer structure and one of the layers made of a low hardness material.
JP 2005-195679 A JP 2004-191659 A

  However, even in the elastic body used for the intermediate transfer belt described in the above-mentioned patent document, there are cases where there is a limit to the followability of the embossed paper to the concave portion. As described above, in the conventional image forming apparatus, image quality deterioration may occur depending on the type of the recording medium that is an image forming target.

  According to the image forming apparatus of the present invention, it is an object to provide an image forming apparatus capable of suppressing image quality deterioration regardless of the type of recording medium to be image formed.

The image forming apparatus of the present invention includes a photosensitive member, a latent image forming unit that forms an electrostatic latent image on the photosensitive member by exposing the photosensitive member, and the electrostatic latent image on the photosensitive member by toner. Developing means for developing and forming a toner image, an intermediate transfer belt to which the toner image conveyed in a predetermined direction and formed on the photosensitive member is transferred, and an electric field having a predetermined first electric field strength. By forming between the intermediate transfer belt and the intermediate transfer belt, the first transfer means for transferring the toner image transferred to the intermediate transfer belt to a recording medium, and the conveyance of the intermediate transfer belt from the first transfer means And an electric field having a second electric field strength larger than the first electric field strength. The intermediate transfer belt is sandwiched between the roll and the backup roll disposed opposite to the roll. The intermediate transfer By forming between the belt, and a and a second transfer unit that transfers the toner image transferred to the intermediate transfer belt to a recording medium.
The roll as the second transfer means is preferably a roll formed by forming a urethane foam layer on a cored bar.
In the image forming apparatus of the present invention is capable of transferring all the toner first field strength constitutes a toner image of a low concentration below the recording medium, and high concentrations of the following A portion of the toner constituting the toner image is transferred to the recording medium, but all of the toner constituting the high-density toner image cannot be transferred to the recording medium . The electric field strength of 2 is an electric field strength at which all the toner constituting the high-density toner image can be transferred to the recording medium only by the second transfer means .
Low density toner image: Toner image having a density of less than 40% when the maximum density of the image that can be formed is 100% High toner image: The maximum density of the image that can be formed is a density of 100% Sometimes a toner image with a density of 40% or more

  In the image forming apparatus of the present invention, a first voltage applying unit that applies a first voltage predetermined in accordance with the first electric field strength to the first transfer unit, and the second electric field strength. And a second voltage applying means for applying a second voltage predetermined in accordance with the second transferring means. The absolute value of the second voltage is larger than the absolute value of the first voltage.

  In the image forming apparatus of the present invention, the second transfer unit includes a plurality of small transfer units arranged along the conveyance direction of the intermediate transfer belt, and is provided on the upstream side in the conveyance direction of the intermediate transfer belt. The electric field strength of the electric field formed with the intermediate transfer belt is large from the small transfer unit toward the small transfer unit provided on the downstream side.

  In the image forming apparatus of the present invention, the second transfer unit may be either an electric field forming region for forming an electric field with the intermediate transfer belt or a separated region separated from the electric field forming region. The moving means which moves so that it may become can be provided.

  The image forming apparatus according to the present invention includes an acquisition unit that acquires type information indicating a type of a recording medium that is an object of image formation, and information indicating that the type information acquired by the acquisition unit indicates a recording medium having irregularities. And a control means for controlling the moving means to move the second transfer means to the electric field forming region.

  As described above, according to the image forming apparatus of the present invention, it is possible to provide an image forming apparatus capable of suppressing image quality deterioration regardless of the type of recording medium to be image formed.

  An image forming apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

  As shown in FIG. 1, an image forming apparatus 10 according to the present embodiment is a quadruple tandem color copier, and each color of yellow (Y), magenta (M), cyan (C), and black (K). The yellow image forming unit 11Y, the magenta image forming unit 11M, the cyan image forming unit 11C, and the black image forming unit 11K (hereinafter collectively referred to as the image forming unit 11) for forming the toner image are described in detail. They are arranged side by side along the moving direction of an intermediate transfer belt 30 described later.

  The yellow image forming unit 11Y is provided with a photoconductor 12Y as a photoconductor. The photoconductor 12Y is rotated at a predetermined process speed in a direction indicated by an arrow (right rotation direction) by a motor (not shown). Driven.

  Around the photoconductor 12Y, a charging device including the charging roll 14Y, an exposure device 13Y, and a developing device 15Y are sequentially arranged along the rotation direction of the photoconductor 12Y.

  The charging roll 14Y is provided in contact with the surface of the photoreceptor 12Y, and charges the surface of the photoreceptor 12Y to a uniform charging potential. The exposure device 13Y irradiates the surface of the photoconductor 12Y charged by the charging device with a laser beam L modulated based on image data of an image corresponding to the Y color of the image to be formed. An electrostatic latent image is formed thereon.

  Two-component developer is stored in the developing device 15Y. As the two-component developer, a known two-component developer including a toner and a carrier can be applied. The two-component developer is stored in a state of being charged to a predetermined charge amount by being stirred by a mechanism (not shown) in the developing device 15Y. The developing device 15Y includes a developing roll 16Y for developing the electrostatic latent image formed on the photoreceptor 12Y with Y (yellow) toner. The developing roller 16Y carries the two-component developer stored in the developing device 15Y and supplies it from the developing device 15Y to the surface of the photoreceptor 12Y, thereby developing the two-component development on the electrostatic latent image on the photoreceptor 12Y. The toner of the agent is adhered by electrostatic force. As a result, the electrostatic latent image on the photoreceptor 12Y is developed by the toner supplied from the developing roll 16Y, and a toner image corresponding to the electrostatic latent image is formed on the photoreceptor 12Y.

  A primary transfer roll 18Y is provided on the downstream side in the rotation direction of the photoconductor 12Y from the position where the developing device 15Y is disposed around the photoconductor 12Y. The primary transfer roll 18Y is disposed to face the photoconductor 12Y with the intermediate transfer belt 30 interposed therebetween. A primary transfer bias having a polarity (for example, positive polarity) opposite to that of the toner carried on the photoreceptor 12Y is applied to the primary transfer roll 18Y by a voltage application member (not shown).

  The contact area between the photoreceptor 12Y and the intermediate transfer belt 30 will be referred to as a primary transfer area T1.

  A cleaning device 20Y for removing deposits such as toner on the photoconductor 12Y is disposed downstream of the primary transfer region T1 in the rotation direction of the photoconductor 12Y.

  The cleaning device 20Y is pressed against the outer peripheral surface of the photoconductor 12Y and rotationally driven in a direction opposite to the rotation direction of the photoconductor 12Y, and scrapes off deposits such as transfer residual toner from the photoconductor 12Y.

Similar to the yellow image forming unit 11Y, the magenta image forming unit 11M includes a photoconductor 12M, and a charging device and an exposure device 13M including a charging roll 14M are provided around the photoconductor 12M. The developing roller 16M, the primary transfer roller 18M, and the cleaning device 20M of the developing device 15M are sequentially arranged along the rotation direction of the photoconductor 12M.
It should be noted that the charging device including the photoconductor 12M and the charging roller 14M, the exposure device 13M, the developing roller 16M of the developing device 15M, the primary transfer roller 18M, and the cleaning device 20M each include the yellow image forming unit 11Y. Are the same mechanisms as the charging device including the photoconductor 12Y and the charging roll 14Y, the exposure device 13Y, the developing roll 16Y of the developing device 15Y, the primary transfer roll 18Y, and the cleaning device 20Y. The detailed explanation is omitted.
The difference from the yellow image forming unit 11Y is that the magenta image forming unit 11M is an image forming unit for forming a magenta color image. Specifically, the exposure device 13M irradiates the surface of the photoreceptor 12M charged by the charging device with a laser beam L modulated based on image data of an image corresponding to the M color of the image to be formed. Thus, an electrostatic latent image is formed on the photoconductor 12M. Further, magenta toner is stored in the developing device 15M, and the developing roller 16M develops the electrostatic latent image formed on the photoreceptor 12M with M (magenta) toner.

Similar to the yellow image forming unit 11Y, the cyan image forming unit 11C includes a photoconductor 12C, and a charging device and an exposure device 13C including a charging roll 14C are provided around the photoconductor 12C. A developing roller 16C, a primary transfer roller 18C, and a cleaning device 20C of the developing device 15C are sequentially arranged along the rotation direction of the photoconductor 12C.
Note that each of the photosensitive member 12C, the charging device including the charging roller 14C, the exposure device 13C, the developing roller 16C of the developing device 15C, the primary transfer roller 18C, and the cleaning device 20C includes the yellow image forming unit 11Y. Are the same mechanisms as the charging device including the photoconductor 12Y and the charging roll 14Y, the exposure device 13Y, the developing roll 16Y of the developing device 15Y, the primary transfer roll 18Y, and the cleaning device 20Y. The detailed explanation is omitted.
The difference from the yellow image forming unit 11Y is that the cyan image forming unit 11C is an image forming unit for forming a cyan image. Specifically, the exposure device 13C irradiates the surface of the photoreceptor 12C charged by the charging device with laser light L modulated based on image data of an image corresponding to the cyan color of the image to be formed. Thus, an electrostatic latent image is formed on the photoconductor 12C. Further, cyan toner is stored in the developing device 15C, and the developing roller 16C develops the electrostatic latent image formed on the photoreceptor 12C with C (cyan) toner.

Similar to the yellow image forming unit 11Y, the black image forming unit 11K includes a photoconductor 12K, and a charging device and an exposure device 13K including a charging roll 14K are provided around the photoconductor 12K. The developing roll 16K, the primary transfer roll 18K, and the cleaning device 20K of the developing device 15K are sequentially arranged along the rotation direction of the photoconductor 12K.
It should be noted that the charging device including the photoconductor 12K and the charging roller 14K, the exposure device 13K, the developing roller 16K of the developing device 15K, the primary transfer roller 18K, and the cleaning device 20K each include the yellow image forming unit 11Y. Are the same mechanisms as the charging device including the photoconductor 12Y and the charging roll 14Y, the exposure device 13Y, the developing roll 16Y of the developing device 15Y, the primary transfer roll 18Y, and the cleaning device 20Y. The detailed explanation is omitted.
The difference from the yellow image forming unit 11Y is that the black image forming unit 11K is an image forming unit for forming a black image. Specifically, the exposure device 13K irradiates the surface of the photoreceptor 12K charged by the charging device with a laser beam L modulated based on image data of an image corresponding to the K color of the image to be formed. Thus, an electrostatic latent image is formed on the photoreceptor 12K. Further, black toner is stored in the developing device 15K, and the developing roller 16K develops the electrostatic latent image formed on the photoconductor 12K with K-color (black) toner.

  In the following description, the members having the same function provided in each of the yellow image forming unit 11Y, the magenta image forming unit 11M, the cyan image forming unit 11C, and the black image forming unit 11K are collectively referred to as Y, M. , C, and K are abbreviated and described. That is, when the photoconductor 12Y, the photoconductor 12M, the photoconductor 12C, and the photoconductor 12K are collectively referred to as the photoconductor 12, they are collectively referred to as the charging roll 14Y, the charging roll 14M, the charging roll 14C, and the charging roll 14K. In this case, it is referred to as the charging roll 14, and when the exposure device 13Y, the exposure device 13M, the exposure device 13C, and the exposure device 13K are collectively referred to as the exposure device 13, the development device 15Y, the development device 15M, and the development device 15C. , And the developing device 15K are collectively referred to as the developing device 15, and the developing roller 16Y, the developing roller 16M, the developing roller 16C, and the developing roller 16K are collectively referred to as the developing roller 16, and the primary transfer roller. 18Y, primary transfer roll 18M, primary transfer roll 18C, and primary transfer roll 18K are collectively referred to as primary transfer. Called Lumpur 18, a cleaning device 20Y, a cleaning device 20M, when little cleaning device 20C, and a cleaning device 20K will be described with referred to as a cleaning device 20.

  The intermediate transfer belt 30 is wound around a drive roll 32, an upstream secondary transfer backup roll 34, a downstream secondary transfer backup roll 60, and a stretching roll 33. The intermediate transfer belt 30 is stretched by these driving rolls 32, the upstream secondary transfer backup roll 34, the downstream secondary transfer backup roll 60, and the stretching roll 33 so as not to be loosened. Further, when the driving roll 32 rotates in the opposite direction to the rotation direction of the photosensitive member 12 with the intermediate transfer belt 30 stretched, the intermediate transfer belt 30 is rotated along with the rotation of the driving roll 32. It is rotated and conveyed in the direction opposite to the rotation direction of the photoconductor 12. That is, in the closest region (primary transfer region T1) between the photoconductor 12 and the intermediate transfer belt 30, the movement direction of the intermediate transfer belt 30 and the photoconductor 12 is the same.

  The yellow image forming unit 11Y, the magenta image forming unit 11M, the cyan image forming unit 11C, and the black image forming unit 11K are arranged in series in that order in the moving direction of the intermediate transfer belt 30. As a result, the toner image on the photoreceptor 12 is primarily transferred onto the intermediate transfer belt 30 in the order of yellow, magenta, cyan, and black by the primary transfer roll 18 in each primary transfer region T1.

  In the vicinity of the upstream secondary transfer backup roll 34, an upstream secondary transfer roll 36 is disposed opposite to the intermediate transfer belt 30. The upstream secondary transfer roll 36 corresponds to the first transfer unit of the present invention, and is provided so as to sandwich the intermediate transfer belt 30 with the upstream secondary transfer backup roll 34.

The downstream secondary transfer backup roll 60 is provided on the downstream side in the transport direction of the intermediate transfer belt 30 from the upstream secondary transfer backup roll 34.
In the vicinity of the downstream secondary transfer backup roll 60, a downstream secondary transfer roll 62 is disposed so as to face the intermediate transfer belt 30. The downstream side secondary transfer roll 62 corresponds to the second transfer unit of the present invention, and is provided so as to sandwich the intermediate transfer belt 30 with the downstream side secondary transfer backup roll 60.

  Below the intermediate transfer belt 30, a paper feed tray 42 for storing the recording medium P is disposed, and in the vicinity of the paper feed tray 42, the recording medium P is sent from the paper feed tray 42 to the paper transport path 40. Feed rolls 44, and a retard roll 46 for separating the recording medium P to be fed out one by one.

  The recording medium P sent out from the paper feed tray 42 to the paper transport path 40 is moved along the intermediate transfer belt 30 and the upstream secondary transfer roll 36 by rollers and rollers 47 (not shown) provided along the paper transport path 40. , The intermediate transfer belt 30 and the downstream secondary transfer roll 62 (hereinafter referred to as the downstream secondary transfer region T3) after being conveyed to the opposite region (hereinafter referred to as the upstream secondary transfer region T2). ).

  A first voltage for applying to the upstream side secondary transfer roll 36 a first voltage having a polarity opposite to that of the toner constituting the toner image carried on the intermediate transfer belt 30 is applied to the upstream side secondary transfer roll 36. The application unit 64 is electrically connected.

  The downstream secondary transfer roll 62 is applied with a second voltage having a polarity opposite to that of the toner constituting the toner image carried on the intermediate transfer belt 30 to the downstream secondary transfer backup roll 60. A voltage application unit 66 is provided.

  The first voltage causes at least a part of the toner constituting the toner image carried on the intermediate transfer belt 30 to move to the recording medium P conveyed to the upstream side secondary transfer region T2 by electrostatic force. An electric field having a possible electric field strength is a voltage that can be formed between the intermediate transfer belt 30 and the recording medium P.

  The second voltage is an electric field strength capable of moving the toner image carried on the intermediate transfer belt 30 to the recording medium P conveyed to the downstream side secondary transfer region T3 by electrostatic force, In addition, the electric field having an electric field strength larger than the electric field strength of the upstream secondary transfer region T2 can be formed in the downstream secondary transfer region T3 between the intermediate transfer belt 30 and the recording medium P.

  For this reason, the absolute value of the second voltage is set in advance so as to be larger than the absolute value of the first voltage.

  The voltage value of each of the first voltage and the second voltage is determined based on the charge amount μc / g of the toner carried on the intermediate transfer belt 30, the charge amount distribution, and a voltage having a predetermined intensity on the upstream side. The electric field strength of the electric field formed in the upstream secondary transfer region T2 when applied to the transfer roll 36, and the downstream secondary transfer region T3 when a voltage having a predetermined strength is applied to the downstream secondary transfer roller 62. And the electric field strength of the electric field formed in advance.

For example, when the maximum density of an image that can be formed by the image forming apparatus 10 is 100%, an image having a density of less than 40% is defined as “low density”.
Then, the electric field intensity capable of transferring (transferring) the toner constituting the low-density toner image transferred from the photoreceptor 12 onto the intermediate transfer belt 30 to the recording medium P in the upstream secondary transfer region T2. Determine. This electric field strength can be obtained based on the charge amount distribution of the toner constituting the low density toner image.
The voltage value of the first voltage may be determined as a voltage having such a strength that an electric field having the determined electric field strength can be formed in the upstream secondary transfer region T2.

Further, when the maximum density of an image that can be formed by the image forming apparatus 10 is 100%, an image having a density of 40% or more is defined as “high density”.
Then, the electric field intensity is determined that allows the toner constituting the high-density toner image transferred from the photoreceptor 12 to the intermediate transfer belt 30 to be transferred to the recording medium P in the downstream secondary transfer region T3. This electric field strength can be determined based on the charge amount distribution of the toner constituting the high-density toner image.
The voltage value of the second voltage may be determined as a voltage having a strength capable of forming the electric field having the determined electric field strength in the downstream side secondary transfer region T3.

  The voltage value of the first voltage is such that a discharge is generated between each toner constituting the toner image carried on the intermediate transfer belt 30 and the recording medium P in the upstream secondary transfer region T2. In order to suppress the occurrence of the electric field, the electric field intensity is 40 as compared with the electric field strength that can transfer all of the toner constituting the 100% density toner image carried on the intermediate transfer belt 30 to the recording medium P side. It is preferably a voltage value of a voltage that can form an electric field having an electric field strength of less than% in the upstream secondary transfer region T2.

  If the resistances of the secondary transfer backup roll and the secondary transfer roll are equal on the upstream side and the downstream side, the absolute value of the voltage value of the second voltage is 1% of the absolute value of the voltage value of the first voltage. It is essential that it is large in the range of 1000% or less, preferably in the range of 100% or more and 800% or less, and more preferably in the range of 120% or more and 600% or less.

  If the absolute value of the voltage value of the second voltage is 1000% or more larger than the absolute value of the voltage value of the first voltage, there may occur a problem that an image defect occurs due to discharge loss. If so, there may be a problem that the effect of transferring all of the toner to be transferred to the recording medium P cannot be obtained.

  Of the upstream secondary transfer backup roll 34 and the downstream secondary transfer backup roll 60, the upstream secondary transfer backup roll 34 provided facing the upstream secondary transfer roll 36 is a long rail. A guide 72 supported so as to be movable in the longitudinal direction 68 is supported via a holder (not shown).

The guide 72 is provided with a motor 70. The motor 70 is connected to a control unit 76, which will be described later in detail, for controlling various devices provided in the image forming apparatus 10, and is driven by a control signal input from the control unit 76. By driving the motor 70, the upstream side secondary transfer backup roll 34 can move in the longitudinal direction of the long rail 68.
That is, the upstream secondary transfer backup roll 34 is provided so as to be movable in both directions from one end of the long rail 68 in the longitudinal direction to the other end.

  The long rail 68 is positioned so that the upstream secondary transfer backup roll 34 can be moved in the long direction of the long rail 68 while maintaining a state where a constant tension is applied to the intermediate transfer belt 30. Is provided. In this embodiment, the case where the long rail 68 is a straight line will be described. However, the upstream secondary transfer backup roll 34 can be moved while the intermediate transfer belt 30 is kept stretched. If it exists, it may be curved, wavy, etc., and is not limited to a straight line.

  In the present embodiment, when the upstream secondary transfer backup roll 34 is positioned at one end of the long rail 68 in the longitudinal direction (area A in FIGS. 1 and 2, hereinafter referred to as an electric field forming area), The transfer belt 30 is pressed toward the upstream secondary transfer roll 36 by the upstream secondary transfer backup roll 34. That is, when the upstream secondary transfer backup roll 34 is positioned in the electric field forming area A, the upstream secondary transfer roll 36 is transferred to the intermediate transfer belt 30 via the recording medium P conveyed to the upstream secondary transfer area T2. An electric field can be formed between the two.

  On the other hand, as shown in FIG. 2, the upstream secondary transfer backup roll 34 is provided at the other end of the long rail 68 in the longitudinal direction (region B in FIGS. 1 and 2, hereinafter referred to as the separation region B). When positioned, the intermediate transfer belt 30 is released from the state of being pressed toward the upstream secondary transfer roll 36 by the upstream secondary transfer backup roll 34, and the intermediate transfer belt 30 and the upstream secondary transfer roll 36 are released. Between the two, a gap is formed so that an electric field cannot be formed even when a voltage is applied to the upstream side secondary transfer roll 36. That is, when the upstream secondary transfer backup roll 34 is located in the separation area, the upstream secondary transfer roll 36 is connected to the intermediate transfer belt 30 via the recording medium P conveyed to the upstream secondary transfer area T2. It becomes impossible to form an electric field between them.

  As described above, when the upstream secondary transfer backup roll 34 is moved in the longitudinal direction of the long rail 68 by driving the motor 70 and is positioned in the electric field forming region or the separation region, the image forming apparatus 10 Two states can be formed between the upstream secondary transfer roll 36 and the intermediate transfer belt 30, a state where an electric field can be formed and a state where an electric field is difficult to form.

  When the toner image carried on the intermediate transfer belt 30 reaches the upstream secondary transfer region T2 and the recording medium P reaches the upstream secondary transfer region T2, it is carried on the intermediate transfer belt 30. At least a part of the toner constituting the toner image is secondarily transferred to the recording medium P. Further, the toner image carried on the intermediate transfer belt 30, that is, the toner image held on the intermediate transfer belt 30 even after passing through the upstream secondary transfer region T 2, is transferred to the downstream secondary transfer region T 3. When the recording medium P reaches the downstream secondary transfer area T3, the toner image carried on the intermediate transfer belt 30 is transferred in the upstream secondary transfer area T2 on the recording medium P. The toner image is secondarily transferred so as to overlap the toner image.

  Note that the toner image is transferred to the recording medium P in the downstream secondary transfer region T3 so that the toner image is transferred to the recording medium P in the upstream secondary transfer region T2, and is positioned in the electric field forming region. It is assumed that the distance between the upstream secondary transfer roll 36 and the downstream secondary transfer backup roll 60 and the conveyance speed of the recording medium P are determined in advance.

  A fixing device 50 is provided on the downstream side in the transport direction of the recording medium P from the installation position of the downstream side secondary transfer roll 62 on the paper transport path 40.

  The fixing device 50 is configured to include a heating roll 52 and a pressure roll 54 that are disposed to face each other via the paper conveyance path 40. A discharge roll 56 for discharging the recording medium P to the outside of the image forming apparatus 10 is provided on the downstream side in the conveyance direction of the recording medium P from the installation position of the fixing device 50. The paper transport path 40 extends from the feed roll 44 and the retard roll 46 to the discharge roll 56 via the upstream secondary transfer region T2 and the fixing device 50.

  When the recording medium P to which the toner image has been transferred by passing through the upstream secondary transfer area T2 and the downstream secondary transfer area T3 is conveyed to the installation position of the fixing device 50, the recording medium P is fixed to the recording medium P. The device 50 applies heat or heat and pressure. The toner image on the recording medium P is fixed on the recording medium P by applying heat or heat and pressure. Thereby, an image is formed on the recording medium P. The recording medium P on which the image is formed is discharged to the outside of the image forming apparatus 10 by the discharge roll 56.

  An intermediate transfer belt cleaner 38 is provided in contact with the surface of the intermediate transfer belt 30 via the intermediate transfer belt 30 in the vicinity of the tension roll 33 that stretches the intermediate transfer belt 30. When the intermediate transfer belt 30 is conveyed in a predetermined direction, deposits such as toner on the intermediate transfer belt 30 are removed from the intermediate transfer belt 30 in a contact area with the intermediate transfer belt cleaner 38.

  The image forming apparatus 10 includes a control unit 76 for controlling the entire image forming apparatus 10. The control unit 76 is connected to the motor 70 and various devices in the image forming apparatus 10 so as to be able to exchange signals. The control unit 76 includes an internal memory (not shown), and a processing routine and various data shown in FIG. 3 to be described later are stored in advance in the internal memory.

The image forming apparatus 10 includes an acquisition unit 74 for acquiring information indicating the type of recording medium to be image formed, image data of an image to be formed, and the like.
The acquisition unit 74 may be an input mechanism such as a touch panel or a keyboard, or may be an input / output mechanism for inputting various data from an external device wirelessly or by wire. Information indicating the type of recording medium includes embossed paper information indicating embossed paper, plain paper information indicating plain paper, and the like.

The above-mentioned “embossed paper” is a special paper having an uneven surface, and particularly a recording medium having a surface unevenness difference of 40 μm to 60 μm and a thickness of 100 μm to 260 μm. Examples of such embossed paper include Rezac and the like, and can be obtained as “Rezac 66 (151 g / m2)” manufactured by Fuji Xerox Office Supply.
Further, “plain paper” usually refers to those having a surface unevenness difference of about 10 μm.

  Here, the intermediate transfer belt 30 used in the image forming apparatus 10 according to the present embodiment is a 0.08 mm thick belt made of semiconductive polyimide.

  The photoconductor 12 has a function of forming at least an electrostatic latent image (electrostatic charge image). As the photoreceptor 12, an electrophotographic photoreceptor is preferably exemplified. The electrophotographic photoreceptor has a coating film containing an organic photoreceptor or the like on the outer peripheral surface of a cylindrical conductive substrate. The coating is formed on a cylindrical substrate, if necessary, an undercoat layer, a photosensitive layer including a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material, and a surface layer (surface protection if necessary). Layer) are formed in this order. The order of stacking the charge generation layer and the charge transport layer may be reversed. These are laminated photoconductors in which a charge generation material and a charge transport material are contained in separate layers (charge generation layer, charge transport layer), but both the charge generation material and the charge transport material are the same. A single-layer type photoreceptor included in the above layer may be used, and a laminated photoreceptor is preferable. Further, an intermediate layer may be provided between the undercoat layer and the photosensitive layer. In addition, other types of photosensitive layers such as an amorphous silicon photosensitive film may be used in addition to the organic photoreceptor.

  The charging roll 14 is configured by integrally providing an elastic body layer with a predetermined thickness around a shaft member made of a metal material such as iron or stainless steel, and the elastic body is an EPDM rubber in which carbon or the like is dispersed. A conductive material such as (ethylene propylene rubber) can be used.

  The exposure device 13 is not particularly limited. For example, the surface of the photoconductor 12 can be exposed to a light source such as semiconductor laser light, LED light, and liquid crystal shutter light in a desired image-like manner. System equipment and the like.

  The developing device 15 is not particularly limited as long as it has the above-described function, and can be appropriately selected according to the purpose. A method in which a toner layer made of toner carried on the developing roll 16 contacts the surface of the photoreceptor 12 It may be of a type that does not contact.

  The fixing device 50 is not particularly limited as long as the toner image transferred onto the recording medium P is fixed by heating, pressing, or heating and pressing.

  As long as the cleaning device 20 cleans the residual toner on the surface of the photoconductor 12, a cleaning device using a blade cleaning method, a brush cleaning method, a roll cleaning method, or the like may be selected as appropriate. Among these, it is preferable to use a cleaning blade. Examples of the material for the cleaning blade include urethane rubber, neoprene rubber, and silicon rubber. Among them, it is particularly preferable to use a polyurethane elastic body because of its excellent wear resistance. However, there may be a mode in which the cleaning device 20 is not used when toner having high transfer efficiency is used.

Next, the operation of the image forming apparatus 10 of the present invention will be described.
In the present embodiment, the upstream side secondary transfer roll 36 is always applied with a first voltage having a voltage value determined in advance based on the above-mentioned rules from the first voltage application unit 64, and the downstream side The secondary transfer roll 62 is supplied with a second voltage having a voltage value determined in advance based on the above-mentioned rule (a voltage value having a larger absolute value than the absolute value of the voltage value of the first voltage). It is assumed that the voltage application unit 66 is constantly applied.

  When the control unit 76 acquires image data of an image to be formed through the acquisition unit 74 and acquires type information indicating the type of the recording medium P to be formed with the image, the control unit 76 illustrated in FIG. The processing routine is executed, and the routine proceeds to step 100.

  In step 100, it is determined whether the type information indicating the type of the recording medium acquired by the acquisition unit 74 is plain paper information or embossed paper information.

  If it is determined in step 100 that the type information acquired by the acquisition unit 74 is embossed paper information, the process proceeds to step 104 and the upstream secondary transfer region T2 (upstream secondary transfer roll 36 and intermediate transfer belt 30 A movement signal indicating that the upstream side secondary transfer backup roll 34 is moved to the electric field forming region A is output to the motor 70 so that an electric field can be formed in the region between the two.

The motor 70 that has received the movement signal moves the upstream secondary transfer backup roll 34 to the electric field forming region A.
By the processing in step 104, an electric field is formed between the intermediate transfer belt 30 and the upstream secondary transfer roll 36 (upstream secondary transfer region T <b> 2), and the intermediate transfer belt 30 and the downstream secondary transfer roll 62. In this state, an electric field is formed between (a downstream secondary transfer region T3).

In the next step 106, after executing the image forming process, this routine is finished.
Specifically, in step 106, the yellow image forming unit 11Y, the magenta image forming unit 11M, the cyan image forming unit 11C, and the black image forming unit 11K are respectively Y, M, A signal for forming a toner image of each color of C and K is output to the image forming unit 11 for forming a toner image of the corresponding color.
The intermediate transfer belt 30 is conveyed and sequentially passes through the primary transfer region T1 in each of the yellow image forming unit 11Y, the magenta image forming unit 11M, the cyan image forming unit 11C, and the black image forming unit 11K. A Y-color toner image, an M-color toner image, a C-color toner image, and a K-color toner image are sequentially superimposed and transferred onto the image.

  When the region carrying the toner image on the intermediate transfer belt 30 reaches the upstream secondary transfer region T2 as the intermediate transfer belt 30 is conveyed, it is formed in the upstream secondary transfer region T2 by the upstream secondary transfer roller 36. Due to the applied electric field, at least a part of the toner constituting the toner image is secondarily transferred to the recording medium P conveyed to the upstream side secondary transfer region T2.

  Further, the area on the intermediate transfer belt 30 carrying the toner image composed of the toner that has not been transferred to the recording medium P in the upstream secondary transfer area T2 becomes the downstream secondary transfer area as the intermediate transfer belt 30 is conveyed. When the toner reaches the transfer area T3, the toner constituting the toner image is secondarily transferred to the recording medium P that has been transported to the downstream secondary transfer area T3 after passing through the upstream secondary transfer area T2.

  The image-formed recording medium P is fixed by the fixing device 50 and discharged to the outside of the image forming device 10.

  On the other hand, if it is determined in step 100 that the paper is plain paper information, the process proceeds to step 101.

In step 101, the upstream secondary transfer backup is performed so that an electric field cannot be formed in the upstream secondary transfer region T2 (the region between the upstream secondary transfer roll 36 and the intermediate transfer belt 30). A movement signal indicating that the roll 34 is moved to the separation region B is output to the motor 70.
The motor 70 to which the movement signal is input moves the upstream secondary transfer backup roll 34 from the electric field forming region A to the separated region B while maintaining the tension state of the intermediate transfer belt 30.

  By the processing in step 101, an electric field cannot be formed between the intermediate transfer belt 30 and the upstream secondary transfer roll 36 (upstream secondary transfer region T2), and the intermediate transfer belt 30 and the downstream secondary transfer. An electric field is formed only between the roll 62 (downstream secondary transfer region T3).

In the next step 102, after executing the image forming process, this routine is finished.
Specifically, in step 102, the yellow image forming unit 11Y, the magenta image forming unit 11M, the cyan image forming unit 11C, and the black image forming unit 11K are acquired from the acquiring unit 74 in substantially the same manner as in step 106 above. Based on the obtained image data, a signal for forming a toner image of each color of Y, M, C, K is output to the image forming unit 11 for forming a toner image of the corresponding color.
The intermediate transfer belt 30 is conveyed and sequentially passes through the primary transfer region T1 in each of the yellow image forming unit 11Y, the magenta image forming unit 11M, the cyan image forming unit 11C, and the black image forming unit 11K. A Y-color toner image, an M-color toner image, a C-color toner image, and a K-color toner image are sequentially superimposed and transferred onto the image.

  When the region carrying the toner image on the intermediate transfer belt 30 reaches the downstream secondary transfer region T3 as the intermediate transfer belt 30 is conveyed, the toner constituting the toner image is transferred to the upstream secondary transfer region T2. And then secondarily transferred to the recording medium P conveyed to the downstream secondary transfer region T3.

  In the image forming process of step 102, the upstream secondary transfer region T2 is not formed with an electric field capable of transferring the toner on the intermediate transfer belt 30 to the recording medium P in the upstream secondary transfer region T2. At T2, the toner on the intermediate transfer belt 30 does not move to the recording medium P.

  The image-formed recording medium P is fixed by the fixing device 50 and discharged to the outside of the image forming device 10.

  As described above, according to the image forming apparatus 10 of the present invention, the toner image transferred onto the intermediate transfer belt 30 is transferred to the recording medium P when the image is formed on the embossed paper having the uneven surface. In the secondary transfer, the toner image is transferred in two stages by the upstream secondary transfer roll 36 and the downstream secondary transfer roll 62, and between the upstream secondary transfer roll 36 and the intermediate transfer belt 30. The electric field strength of the electric field formed between the downstream secondary transfer roll 62 and the intermediate transfer belt 30 is larger than the electric field strength of the formed electric field.

Since the electric field strength of the electric field formed in the upstream secondary transfer region T2 and the downstream secondary transfer region T3 is determined in this way, the density of the toner image on the intermediate transfer belt 30 is lower than the predetermined density. Is transferred to the recording medium P in the upstream secondary transfer region T2, and the toner constituting the region having a higher density than the predetermined density in the toner image is transferred in the downstream secondary transfer region T3. Transferred to the recording medium P.
In the image formation on the embossed paper, at the time of transfer in the downstream side secondary transfer region T3, since the low-density toner has already been transferred to the recording medium P, the discharge generated in the downstream side secondary transfer region T3 is The toner is transferred between the toner transferred onto the recording medium P and the intermediate transfer belt 30.
Due to the occurrence of this discharge, the toner transferred onto the recording medium P is strongly adhered to the recording medium P, so that the toner transferred onto the recording medium P can be prevented from transferring to the intermediate transfer belt 30.

  Therefore, in the image formation on the embossed paper, it is possible to realize good transfer to the recording medium for both the high density image and the low density image, and it is possible to suppress image quality deterioration.

  Here, as in the prior art, when secondary transfer is performed using only one of the upstream secondary transfer roll 36 and the downstream secondary transfer roll 62, the embossed paper is used during secondary transfer. Discharge occurs between the concave portion of the recording medium P and the toner carried on the intermediate transfer belt 30. For this reason, the toner on the intermediate transfer belt 30 may be charged with a polarity opposite to the polarity before reaching the secondary transfer region, and transfer to the recording medium P may be inhibited and remain on the intermediate transfer belt 30. is there. For this reason, image quality deterioration may be caused.

  However, according to the image forming apparatus 10 of the present invention, when an image is formed on an embossed paper having an uneven surface, in the secondary transfer, the upstream secondary transfer roll 36 and the downstream secondary transfer roll 62 The toner image is transferred in two stages, and the electric field strength of the electric field formed between the upstream side secondary transfer roll 36 and the intermediate transfer belt 30 is determined between the downstream side secondary transfer roll 62 and the intermediate transfer belt 30. Since the electric field strength of the electric field formed therebetween is large, image quality deterioration can be suppressed.

Also, depending on the type of the recording medium P, when the type of recording medium comprising an image formation target is a plain paper, of the upstream side secondary transfer roller 36 and the downstream side secondary transfer roller 62, the lower flow Secondary transfer can be performed using only the side secondary transfer roll 62 .

  For this reason, when transferring a toner image to embossed paper, where secondary transfer failure is likely to occur due to the density of the toner image in the secondary transfer, the toner image is transferred in two stages to suppress image quality deterioration. When transferring a toner image onto plain paper that is unlikely to cause a secondary transfer failure due to the density of the toner image during transfer, the downstream secondary transfer of the upstream secondary transfer roll 36 and the downstream secondary transfer roll 62. Since only the roll 62 is used as a mechanism for performing the secondary transfer, image quality deterioration can be suppressed and power consumption can be suppressed as compared with the case where a plurality of secondary transfer rolls are always used.

  Therefore, according to the image forming apparatus 10 of the present invention, it is possible to provide an image forming apparatus capable of suppressing image quality deterioration regardless of the type of recording medium to be image formed.

  In the above embodiment, the case where the secondary transfer is performed using the two mechanisms of the upstream side secondary transfer roll 36 and the downstream side secondary transfer roll 62 as the mechanism for performing the secondary transfer has been described. Secondary transfer may be performed using three or more secondary transfer rolls, and is not limited to two.

In this case, as shown in FIG. 4, the upstream secondary transfer roll 36 includes a plurality of small upstream secondary transfer rolls 36 _{1 to} 36 _n and each of the small upstream secondary transfer rolls 36 _1. to ~ 36 _n voltage application unit ₆₄ 1 to 64 _n for applying a first voltage may be respectively so as to provide correspondingly.

Further, upstream secondary transfer backup rolls 34 _{1 to} 34 _n are provided so as to sandwich the intermediate transfer belt 30 in correspondence with the plurality of small upstream secondary transfer rolls 36 _{1 to} 36 _n, respectively. The upstream secondary transfer backup rolls 34 _{1 to} 34 _n are configured as an upstream secondary transfer backup roll 34 so that the upstream side secondary transfer backup rolls 34 _{1 to} 34 _n can be moved by the motor 70 so as to be in any position of the electric field forming region A and the separation region B. do it.
Then, from the voltage application units 64 ₁ to 64 _n for applying the first voltage to the small upstream side secondary transfer rolls 36 _{1 to} 36 _n , the intermediate transfer belt 30 moves from the upstream side in the conveyance direction to the downstream side. A voltage that increases the strength of the electric field formed between the intermediate transfer belt 30 and the intermediate transfer belt 30 may be applied stepwise or continuously.

With this configuration, images concentration, i.e. it is possible to transfer at an optimum electric field corresponding to the toner layer charge amount, irregularities or larger paper, the image having a variation in the wider toner charge amount In addition, it is possible to obtain an effect that good transfer without image defects such as missing discharge is possible.

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely in detail, the present invention is not limited to the following examples.

Example 1
The upstream secondary transfer is performed as shown in FIG. 1 by modifying the image forming apparatus (manufactured by Fuji Xerox, trade name: Color DocuTech 60 V) to replace the secondary transfer mechanism of the image forming apparatus. Backup roll 34, downstream secondary transfer backup roll 60, upstream secondary transfer roll 36, first voltage application unit 64, downstream secondary transfer roll 62, second voltage application unit 66, long rail 68 A guide 72 and a motor 70 are provided, and the processing routine shown in FIG. 3 is executed by the control unit of the image forming apparatus using embossed paper, and image quality evaluation is performed.

As the embossed paper, “Rezac 66” (surface roughness difference of 80 μm, 151 g / m ² ) manufactured by Fuji Xerox Office Supply Co., Ltd. was used.

The image forming apparatus was operated with the following specifications.
・ Intermediate transfer belt: Made of polyimide
Thickness 0.08mm
Common logarithm of surface resistivity 12 LogΩ / □
Common logarithm of volume resistivity 11 LogΩ · cm
-Image carrier surface moving speed (rotational speed): 260 mm / s
・ Movement speed of intermediate transfer belt 30 surface: 260 mm / s
・ Configuration of upstream side secondary transfer roll 36: Φ21 mm roll having a urethane foam layer formed on a core metal of Φ12 mm ・ Configuration of downstream side secondary transfer roll 62: Φ21 mm having a urethane foam layer formed on a core metal of Φ12 mm Roll and transfer conditions Primary transfer bias: Y color 30 μA, M color 30 μA, C color 30 μA, K color 30 μA
Voltage applied from the first voltage application unit 64 to the upstream side secondary transfer roll 36: 0.3 kV
Voltage applied to the downstream secondary transfer roll 62 from the second voltage application unit 66: 1.5 kV

  The surface resistivity ρs (Ω / □) and the volume resistivity in this example are measured according to JIS K 6991. Circular electrodes (HR probe of Hiresta IP manufactured by Mitsubishi Yuka Co., Ltd .: outside of cylindrical electrode part) Using a diameter of 16 mmφ, an inner diameter of the ring electrode portion of 30 mmφ, and an outer diameter of 40 mmφ, applying a voltage of 100 V in an environment of 22 ° C./55% RH, obtaining a current value after 10 seconds, and calculating using the following formula (1) did.

Formula (1) ρs = π × (D + d) / (D−d) × (V / I)

  The volume resistivity was measured from the current value 30 seconds after 100 V was applied using the ring electrode.

  In the image forming apparatus having the above specifications, the processing routine shown in FIG. 3 is executed, and a three-color solid image area of three colors of Y, M, and C (an image area having a density of 100%, that is, a density of 100). Image area obtained by superimposing a 100% density M color toner image and a 100% density C color toner image on a 100% Y color toner image), and a 30% density highlight image area. Images were printed on the embossed paper and evaluated for image quality.

The image quality evaluation criteria were as follows.
◯: When the output image is good without image omission.
×: When an output image has an image omission.
The evaluation results are shown in Table 1.

(Example 2)
Except that the voltage applied from the second voltage application unit 66 to the downstream side secondary transfer roll 62 was set to 2.0 kV, the image formation processing was performed on the embossed paper in the same manner as in Example 1, and the image quality was evaluated. . The evaluation results are shown in Table 1 below.

(Example 3)
Except that the following intermediate transfer belt was used as the intermediate transfer belt 30, image formation processing was performed on the embossed paper in the same manner as in Example 1, and image quality evaluation was performed. The evaluation results are shown in Table 1.

  The intermediate transfer belt 30 is a 0.55 mm thick elastic belt made of chloroprene having a Young's modulus of 3 MPa as an elastic layer, and two layers in which a 3 μm urethane-based coating layer (surface layer) is formed on the surface of the elastic layer. The structure was used.

Example 4
Except that the voltage applied from the second voltage application unit 66 to the downstream side secondary transfer roll 62 was set to 2.0 kV, the image formation processing was performed on the embossed paper in the same manner as in Example 3 to evaluate the image quality. . The evaluation results are shown in Table 1.

(Comparative Example 1)
Except that the voltage applied to the downstream secondary transfer roll 62 from the second voltage application unit 66 was 0.25 kV, image formation processing was performed on the embossed paper in the same manner as in Example 1, and image quality evaluation was performed. . The evaluation results are shown in Table 1.

(Comparative Example 2)
The first voltage application unit 64 and the upstream secondary transfer roll 36 are removed from the image forming apparatus used in Embodiment 1, and the voltage applied from the second voltage application unit 66 to the downstream secondary transfer roll 62 is applied. Except for setting to 0.5 kV, image formation processing was performed on embossed paper in the same manner as in Example 1, and image quality evaluation was performed. The evaluation results are shown in Table 1.

(Comparative Example 3)
The first voltage application unit 64 and the upstream secondary transfer roll 36 are removed from the image forming apparatus used in Embodiment 1, and the voltage applied from the second voltage application unit 66 to the downstream secondary transfer roll 62 is applied. Except for setting to 1.0 kV, image formation processing was performed on embossed paper in the same manner as in Example 1, and image quality evaluation was performed. The evaluation results are shown in Table 1.

(Comparative Example 4)
The first voltage application unit 64 and the upstream secondary transfer roll 36 are removed from the image forming apparatus used in Embodiment 1, and the voltage applied from the second voltage application unit 66 to the downstream secondary transfer roll 62 is applied. Except that the voltage was set to 1.5 kV, image formation processing was performed on the embossed paper in the same manner as in Example 1, and image quality evaluation was performed. The evaluation results are shown in Table 1.

(Comparative Example 5)
The first voltage application unit 64 and the upstream secondary transfer roll 36 are removed from the image forming apparatus used in Embodiment 1, and the voltage applied from the second voltage application unit 66 to the downstream secondary transfer roll 62 is applied. Except that the voltage was set to 2.0 kV, an image forming process was performed on the embossed paper in the same manner as in Example 1, and the image quality was evaluated. The evaluation results are shown in Table 1.

(Reference Example 1)
The voltage applied from the first voltage application unit 64 to the upstream secondary transfer roll 36 is set to 0 kV, the voltage applied from the second voltage application unit 66 to the downstream secondary transfer roll 62 is set to 1.5 kV, and the image is displayed. Except for using plain paper as a recording medium for recording and printing, image formation processing was performed in the same manner as in Example 1 to evaluate image quality. The evaluation results are shown in Table 2.
As plain paper, “P paper” (surface roughness difference 10 μm, 64 g / m ² ) from Fuji Xerox Office Supply Co. was used.

(Reference Example 2)
Image formation was performed and image quality evaluation was performed in the same manner as in Reference Example 1 except that the voltage applied from the second voltage application unit 66 to the downstream secondary transfer roll 62 was set to 2.0 kV. The evaluation results are shown in Table 2.

  As shown in Table 1, in image formation on embossed paper, the voltage applied to the downstream secondary transfer roll 62 is larger than the voltage applied to the upstream secondary transfer roll 36 as in Examples 1-4. In this case, an image with good image quality could be formed in both the highlight image area and the three-color solid image area.

  On the other hand, as shown in Comparative Examples 2 to 5, when no voltage is applied to the upstream side secondary transfer roll 36 and a constant voltage is applied only to the downstream side secondary transfer roll 62, a highlight image is displayed. Good image quality was not obtained in one or both of the area and the three-color solid image area.

In the transfer of the toner image to the intermediate transfer belt 30 by each color image forming unit 11, the charge amount distribution of the toner constituting the toner image on each photoreceptor 12 and the toner constituting the toner image on the intermediate transfer belt 30 are transferred. The charge amount distribution shows a relationship as shown in FIG.
In FIG. 5, the range indicated by the arrow indicates the toner charge amount distribution range, and the position indicated by the black circle indicates the peak position of the toner charge amount distribution.

  As shown in FIG. 5, a one-color transfer state in which a one-color toner image (for example, a Y-color toner image) is transferred onto the intermediate transfer belt 30, a two-color transfer state in which a two-color toner image is transferred (for example, a Y-color toner image) A state in which the M color toner image is transferred over the color toner image), a three color transfer state in which the three color toner image is transferred (for example, the M color toner image and the Y color toner image A state in which the C color toner image is transferred in a superimposed manner), and a four color transfer state in which the four color toner images are transferred (for example, an M color toner image, a C color toner image, And a state in which the K color toner images are transferred in a superimposed manner) and a state in which the toner images are formed on the respective photoreceptors, the charge amount distribution of the toner constituting the toner images on the photoreceptor and the intermediate transfer belt 30. Is wider on the intermediate transfer belt than on the photoreceptor, and more More becomes four color transfer state charge amount distribution of the toner is wide, also the charge amount corresponding to the peak is larger from.

  This is considered to be due to the fact that the toner image of a plurality of colors is transferred in an overlapping manner, so that the change in the charge amount of the toner constituting the toner image increases and the charge amount increases.

In Comparative Examples 2 to 5, in the secondary transfer, for example, a K highlight area having a small number of transfers and a small amount of toner, for example, and a three-color solid image area having a large number of transfers and a large amount of toner are mixed. Since the secondary transfer is performed by the voltage applied to the downstream-side secondary transfer roll 62 even in the case of the selected image, as shown in Comparative Example 2, the voltage has a strength capable of obtaining a good image quality for the highlight image region. Is applied to the downstream side secondary transfer roll 62, an electric field for sufficiently transferring the toner image of the three-color solid image to the recording medium P cannot be formed. Further, as shown in Comparative Example 4 and Comparative Example 5, when an electric field having a strength capable of obtaining good image quality is applied to the downstream secondary transfer roll 62 for the three-color solid image region, the highlight image region is transferred. In this case, an excessive electric field is formed, and good image quality cannot be obtained.
For this reason, it is thought that a result as shown in Table 1 is obtained.

  Further, as shown in Comparative Example 1, a voltage applied from the second voltage application unit 66 to the downstream secondary transfer roll 62 from a voltage applied from the first voltage application unit 64 to the upstream secondary transfer roll 36. In the case of the smaller one, it was impossible to form an image with good image quality in the three-color solid image region.

  When plain paper is used as the recording medium, an electric field cannot be formed between the upstream secondary transfer roll 36 and the intermediate transfer belt 30 by executing the processing routine shown in FIG. Since the position of the upstream side secondary transfer backup roll 34 moves from the electric field forming region A to the separation region B, as shown in Reference Example 1 and Reference Example 2 in Table 2, it is applied to the downstream side secondary transfer roll 62. The toner image on the intermediate transfer belt 30 is transferred to the recording medium P only by the electric field formed in the downstream secondary transfer region T3 by the applied voltage. In this case, as shown in Reference Example 1 and Reference Example 2, good image quality was obtained in both the highlight image region and the three-color solid image region.

  For this reason, as shown in Reference Example 1 and Reference Example 2, the downstream secondary transfer roll 62 is used for plain paper that does not have the possibility of image quality deterioration due to secondary transfer failure with respect to the embossed paper having irregularities on the surface. Since the secondary transfer can be performed using only the secondary transfer roller 36, the power consumption can be suppressed compared to the case where the secondary transfer is always performed using the upstream side secondary transfer roll 36 and the downstream side secondary transfer roll 62. It can be said that good image quality can be obtained.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. 4 is a flowchart illustrating processing executed by a control unit of the image forming apparatus according to the embodiment of the present invention. FIG. 3 is a schematic diagram showing a form different from FIGS. 1 and 2 of the image forming apparatus according to the embodiment of the present invention, and is a schematic configuration diagram showing only a secondary transfer region. FIG. 4 is a schematic diagram illustrating a toner charge amount in a toner image formed on a photoreceptor and a toner image formed on an intermediate transfer belt.

Explanation of symbols

10 Image forming device 12, 12Y, 12M, 12C, 12K Photoconductor 13, 13Y, 13M, 13C, 13K Exposure device 14, 14Y, 14M, 14C, 14K Charging roll 15, 15Y, 15M, 15C, 15K Developing device 36 Upstream Side secondary transfer roll 62 Downstream side secondary transfer roll

Claims (2)

A photoreceptor,
Latent image forming means for forming an electrostatic latent image on the photosensitive member by exposing the photosensitive member;
Developing means for developing the electrostatic latent image on the photoreceptor with toner to form a toner image;
An intermediate transfer belt which is conveyed in a predetermined direction and onto which the toner image formed on the photoconductor is transferred;
A first transfer means for transferring the toner image transferred to the intermediate transfer belt to a recording medium by forming an electric field having a predetermined first electric field strength with the intermediate transfer belt;
The roll is provided downstream of the first transfer unit in the conveyance direction of the intermediate transfer belt, and the roll holds the intermediate transfer belt between a backup roll disposed opposite to the intermediate transfer belt. A second transfer means for transferring the toner image transferred to the intermediate transfer belt to a recording medium by forming an electric field having a second electric field strength higher than the first electric field strength with the intermediate transfer belt; ,
An image forming apparatus comprising:
The first electric field strength can transfer all of the toner constituting the low density toner image shown below to the recording medium , and a part of the toner constituting the high density toner image shown below Is transferred to the recording medium, but it is impossible to transfer all of the toner constituting the high-density toner image to the recording medium. The second electric field intensity is the second transfer intensity. images forming device you being a field strength capable of transcribing all of the toner constituting the toner image of the high concentration only by means on the recording medium.
Low density toner image: Toner image having a density of less than 40% when the maximum density of the image that can be formed is 100% High toner image: The maximum density of the image that can be formed is a density of 100% Sometimes a toner image with a density of 40% or more   The image forming apparatus according to claim 1, wherein the roll is a roll formed by forming a urethane foam layer on a cored bar.

Images