JP2018151444A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a reduction in transfer efficiency while reducing the occurrence of an image defect even when an influence factor is changed, compared with a case where the angle of a recording medium to which a toner image is transferred with respect to an intermediate transfer belt is fixed.SOLUTION: A control device moves a post roller 110 downward so as to reduce a wrap angle θ when continuous paper P is a film with a large volume resistivity.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus.

  Patent Document 1 discloses a technique related to a transfer unit that transfers a toner image formed on a toner image carrier to a transfer material. In this prior art, the configuration of the conductive rubber roller and the conductive belt is such that the contact nip region width between the conductive belt and the continuous paper in the transfer portion is narrower than the contact nip region width between the paper and the toner image carrier. (Thickness, rubber hardness, etc.), the pressure contact force of the conductive rubber roller to the paper and the toner image carrier is optimized.

Japanese Patent No. 4939815

  In the transfer of a toner image from an intermediate transfer belt to a recording medium, the transfer efficiency may be lowered if conditions that affect the transfer efficiency are changed.

  In the present invention, compared with the case where the angle of the recording medium onto which the toner image is transferred is fixed with respect to the intermediate transfer belt, the transfer efficiency is suppressed while suppressing the occurrence of image defects even if the conditions affecting the transfer efficiency are changed. The purpose is to suppress the decrease of the above.

  According to a first aspect of the present invention, there is provided an endless intermediate transfer belt to which a toner image formed on an image carrier is transferred, transfer means for transferring the toner image from the intermediate transfer belt to a recording medium, An image forming apparatus comprising: an angle changing unit that is provided on a downstream side in the conveyance direction of the recording medium and changes an angle of the recording medium on which the toner image is transferred with respect to the intermediate transfer belt.

  According to a second aspect of the present invention, in the first aspect, the angle changing unit reduces the angle when the volume resistivity of the recording medium is smaller than that when the volume resistivity is large within a range that does not fall below a predetermined angle. An image forming apparatus.

  According to a third aspect of the present invention, the angle changing means reduces the angle when the toner image contains less low-charged toner than when the toner image does not contain low-charged toner, within a range that does not fall below a predetermined angle. An image forming apparatus according to claim 1.

  According to a fourth aspect of the present invention, in the third aspect, the angle changing means reduces the angle when the ratio of the low-charged toner in the toner image is larger than when the ratio is small, as long as the angle does not fall below a predetermined angle. The image forming apparatus described.

  According to a fifth aspect of the present invention, the angle changing means reduces the angle when the amount per unit area of the low-charged toner in the toner image is larger than that when the amount is smaller than a predetermined angle. An image forming apparatus according to claim 3.

  According to a sixth aspect of the present invention, the angle changing means reduces the angle in the case where the toner image does not contain toner containing titanium oxide in a range that does not fall below a predetermined angle. The image forming apparatus according to claim 1 or 2.

  The invention according to claim 7 is characterized in that the angle changing means reduces the angle when the ratio of the toner containing titanium oxide in the toner image is larger than when the ratio is small within a range that does not fall below a predetermined angle. 6. The image forming apparatus according to 6.

  According to an eighth aspect of the present invention, the angle changing unit reduces the angle when the amount of toner containing titanium oxide in the toner image is larger than when the amount per unit area is small within a range that does not fall below a predetermined angle. An image forming apparatus according to claim 6 or 7.

  The invention according to claim 9 is the image forming apparatus according to any one of claims 6 to 8, wherein the toner containing titanium oxide is a white toner.

  According to a tenth aspect of the present invention, in the first to ninth aspects, the angle changing means reduces the angle when the cumulative image formation time is longer than when the cumulative image formation time is short, as long as the angle does not fall below a predetermined angle. The image forming apparatus according to claim 1.

  According to the first aspect of the present invention, even when the condition that affects the transfer efficiency is changed as compared with the case where the angle of the recording medium onto which the toner image is transferred is fixed with respect to the intermediate transfer belt, the occurrence of image defects occurs. It is possible to suppress a decrease in transfer efficiency while suppressing the above.

  According to the second aspect of the present invention, image defects are generated even when the volume resistivity of the recording medium is changed, as compared with the case where the angle of the recording medium to which the toner image is transferred is fixed with respect to the intermediate transfer belt. While suppressing, a decrease in transfer efficiency can be suppressed.

  According to the third aspect of the present invention, image defects are generated even if the toner image contains low-charged toner as compared with the case where the angle of the recording medium onto which the toner image is transferred is fixed with respect to the intermediate transfer belt. It is possible to suppress a decrease in transfer efficiency while suppressing the above.

  According to the fourth aspect of the present invention, even when the ratio of the low-charged toner in the toner image is changed as compared with the case where the angle of the recording medium onto which the toner image is transferred is fixed with respect to the intermediate transfer belt, the image defect While suppressing the occurrence, it is possible to suppress a decrease in transfer efficiency.

  According to the fifth aspect of the present invention, even when the amount per unit area of the low-charged toner in the toner image is changed, the image defect is not compared with the case where the angle of the recording medium on which the toner image is transferred to the intermediate transfer belt is fixed. While suppressing the occurrence, it is possible to suppress a decrease in transfer efficiency.

  According to the sixth aspect of the present invention, even when the toner image contains a toner containing titanium oxide, the image defect is smaller than when the angle of the recording medium on which the toner image is transferred is fixed with respect to the intermediate transfer belt. It is possible to suppress a decrease in transfer efficiency while suppressing the occurrence of the above.

  According to the seventh aspect of the present invention, even when the ratio of the toner containing titanium oxide in the toner image is changed as compared with the case where the angle of the recording medium onto which the toner image is transferred is fixed with respect to the intermediate transfer belt, It is possible to suppress a decrease in transfer efficiency while suppressing the occurrence of defects.

  According to the eighth aspect of the invention, the ratio of the amount of toner containing titanium oxide per unit area in the toner image is changed as compared with the case where the angle of the recording medium on which the toner image is transferred to the intermediate transfer belt is fixed. In addition, it is possible to suppress a decrease in transfer efficiency while suppressing the occurrence of image defects.

  According to the ninth aspect of the present invention, even when the ratio of the white toner or the amount per unit area is changed as compared with the case where the angle of the recording medium onto which the toner image is transferred is fixed with respect to the intermediate transfer belt, It is possible to suppress a decrease in transfer efficiency while suppressing the occurrence of defects.

  According to the tenth aspect of the present invention, the occurrence of image defects is suppressed even when the cumulative image formation time changes, as compared with the case where the angle of the recording medium onto which the toner image is transferred is fixed with respect to the intermediate transfer belt. However, a decrease in transfer efficiency can be suppressed.

1 is a schematic side view illustrating a configuration of an image forming apparatus according to an embodiment. FIG. 2 is a schematic side view illustrating a configuration of a main part of an image forming apparatus of the image forming apparatus in FIG. 1. FIG. 2 is a schematic side view illustrating a configuration of a main part at a secondary transfer position of the image forming apparatus of FIG. 1. FIG. 2 is a block diagram of a main part of the image forming apparatus in FIG. 1. FIG. 2 is a schematic side view illustrating a configuration of a moving device of the image forming apparatus in FIG. 1. It is a graph which shows the relationship between a wrap angle and transfer efficiency. It is a table | surface which shows the relationship between a paper type, a wrap angle, and an image defect. It is a table | surface which shows the relationship between a paper kind and volume resistivity. It is a graph which shows the relationship between the number of printed sheets and transfer efficiency.

<Overall configuration>
An example of an image forming apparatus according to an embodiment of the present invention will be described.

[Entire configuration of image forming apparatus]
As shown in FIG. 1, an image forming apparatus 10 according to the present exemplary embodiment includes a paper feeding device 12 that feeds a continuous long continuous paper P as an example of a recording medium, and paper feeding from the paper feeding device 12. An image forming unit 14 that forms an image on the continuous paper P that has been formed, a storage device 16 that stores the continuous paper P on which an image has been formed by the image forming unit 14, an operation display unit 19, the paper feeding device 12, and an image And a control device 18 that controls the forming unit 14, the storage device 16, and the operation display unit 19.

  The paper feeding device 12 is provided with a paper feeding roll 20 in which the continuous paper P is wound up in a roll shape. The paper feed roll 20 is rotationally driven by a drive unit (not shown), and the continuous paper P is supplied to the image forming unit 14 via the transport roll pair 80. Note that the direction indicated by the arrow B in FIG. 1 indicates the supply direction of the continuous paper P. A paper feed roll sensor 84 that detects the diameter of the paper feed roll 20 is provided inside the paper feeder 12.

  The continuous paper P uses the word “paper” for the sake of convenience, but is not specified as paper (for example, high-quality paper) mainly composed of fibers such as plants. For example, a film made of a synthetic resin can be used.

  The storage device 16 is provided with a storage roll 22 on which the continuous paper P on which an image has been formed is wound up in a roll shape via a tension applying roll 82 that applies tension to the continuous paper P.

  The image forming unit 14 determines the first white color (W1), the second white color (W2), the yellow color (Y), the magenta color (M), the cyan color (C), and the black color (K) based on the image information. An image using each color toner is formed on the continuous paper P. Since the first white color (W1) and the second white color (W2) are the same white color, they may be referred to as white color (W) (or white (W)) when it is not necessary to distinguish them. is there.

  The white color (W) uses titanium oxide as a pigment. For black (K), carbon black is used as a pigment.

  The image forming unit 14 holds an image forming device 24 for forming a toner image developed with each color toner constituting the developer, and a toner image formed by the image forming device 24, and finally a continuous paper An intermediate transfer device 26 that conveys the toner image conveyed by the intermediate transfer belt 44 of the intermediate transfer device 26 to the continuous paper P; And a fixing device 28 for fixing the toner image on the continuous paper P secondarily transferred by the secondary transfer device 46.

  The image forming device 24 includes six image forming devices 24W1, 24Y, 24M, 24C, 24K, and 24W2 that individually form toner images of colors W1, W2, Y, M, C, and K, respectively. Yes.

  Next, the image forming devices 24W1, 24Y, 24M, 24C, 24K, and 24W2 will be described. Since the configuration is the same except for the type of toner, the description will be made without distinction.

  As shown in FIG. 2, each image forming device 24 includes a photosensitive drum 30 as an example of a rotating image carrier. Around the photosensitive drum 30, a charging device 32, an exposure device 34, a developing device 36, a primary transfer device 38, a cleaning device 40, and the like, which will be described later, are provided.

  The photosensitive drum 30 has an image holding surface having a photoconductive layer (photosensitive layer) (not shown) containing a photosensitive material on the outer peripheral surface (surface) of a cylindrical or columnar substrate that has been grounded. Yes. Further, the photosensitive drum 30 is supported so as to be rotated by transmission of power by a driving device (not shown).

  The charging device 32 includes a contact-type charging roll 32 </ b> A disposed in contact with the photosensitive drum 30, and charges the surface of the photosensitive drum 30 on which an image is formed. A charging voltage is supplied to the charging device 32. When the developing device 36 performs reversal development, a voltage having the same polarity as the charging polarity of the toner supplied from the developing device 36 is applied as the charging voltage. In the present embodiment, the charging polarity of the toner is negative, and the surface of the photosensitive drum 30 is charged negatively.

  The exposure device 34 irradiates the charged surface of the photosensitive drum 30 with light based on image information to form an electrostatic latent image on the surface of the photosensitive drum 30.

  The developing device 36 develops the electrostatic latent image formed on the surface of the photosensitive drum 30 by the exposure device 34 with toner of a corresponding color developer to generate a toner image. Although not shown, the developing device 36 is agitated and conveyed such as a developing roll that conveys the developer to a developing area facing the photosensitive drum 30 and a screw auger that conveys the developer so as to be supplied to the developing roll while stirring the developer. A member and a layer thickness regulating member for regulating the amount of developer held on the developing roll are arranged. A developing bias voltage is applied to the developing device 36 between the developing roll and the photosensitive drum 30. Further, the developing roll and the agitating / conveying member are rotated in a predetermined direction by receiving power from a rotation driving device (not shown). As the developer, for example, a two-component developer containing a nonmagnetic toner and a magnetic carrier may be used. Further, the toner supplied to the developing device 36 is supplied from a toner cartridge 90 (see FIG. 1) containing a developer containing toner of each color.

  The primary transfer device 38 is a contact-type transfer device provided with a primary transfer roll 38A that rotates in contact with the surface of the photosensitive drum 30 via an intermediate transfer belt 44 and is supplied with a primary transfer voltage. . By supplying the primary transfer voltage to the primary transfer roll 38 </ b> A, the toner images of the respective colors formed on the photosensitive drum 30 are transferred to the intermediate transfer belt 44 of the intermediate transfer device 26. In the present embodiment, the primary transfer voltage is a DC voltage having a polarity opposite to the charging polarity of the toner, and the DC voltage is applied to the primary transfer roll 38A.

  Further, the cleaning device 40 removes and removes adherents such as toner remaining on the image holding surface of the photosensitive drum 30 after the primary transfer. In the present embodiment, the cleaning device 40 is provided with a blade 42 that comes into contact with the photosensitive drum 30, and the blade 42 removes deposits attached to the surface of the photosensitive drum 30. .

  As shown in FIG. 1, the intermediate transfer device 26 is disposed at a position below each image forming device 24 (24W1, 24Y, 24M, 24C, 24K, 24W2). In the present embodiment, the intermediate transfer device 26 passes through a primary transfer position between the photosensitive drum 30 and the primary transfer device 38 and rotates in the direction of arrow A in FIG. A plurality of belt support rollers 26A and 26B that rotatably support the transfer belt 44 and a backup roll 72 are mainly provided. Although not shown in the drawings, the intermediate transfer device 26 is cleaned by removing toner and paper dust adhering to the outer peripheral surface of the intermediate transfer belt 44 after passing through the secondary transfer device 46. A belt cleaning device is provided. The backup roll 72 in the secondary transfer device 46 also serves as a belt support roller in the intermediate transfer device 26.

  As the intermediate transfer belt 44, for example, an endless belt made of a material in which a resistance adjusting agent such as carbon black is dispersed in a synthetic resin such as polyimide resin or polyamide resin is used. Further, the intermediate transfer belt 44 is supported by a backup roll 72, a support roller 26A, and a support roller 26B, which will be described later, and is arranged in an inverted triangle shape having the secondary transfer position NT as a vertex as viewed in the axial direction of the backup roll 72. ing.

  The secondary transfer device 46 rotates in contact with the outer peripheral surface of the intermediate transfer belt 44 via the continuous paper P at the secondary transfer position NT of the intermediate transfer belt 44 supported by the backup roll 72 in the intermediate transfer device 26. The contact type transfer device includes a secondary transfer roll 74. Further, a DC voltage having a polarity opposite or the same as the charging polarity of the toner is applied as a secondary transfer voltage to the secondary transfer roll 74 or the backup roll 72 of the intermediate transfer device 26. In the image forming apparatus 10 according to the present embodiment, the toner charging polarity is negative, and a negative DC voltage having the same polarity as the toner charging polarity is applied to the backup roll 72 as a secondary transfer voltage. Applied.

  A density sensor 48 for detecting the density of the toner image transferred to the intermediate transfer belt 44 is provided above the intermediate transfer belt 44. Based on the density detection result of the density sensor 48, toner density is detected. The supply amount is controlled.

  The fixing device 28 has a roll-shaped (or belt-shaped) heating rotator 28A that is heated by heating means so that the surface temperature is maintained at a predetermined temperature, and the heating rotator 28A is predetermined. A roll-shaped (or belt-shaped) pressurizing rotating body 28B that rotates in contact with the continuous paper P by pressure is arranged. In the fixing device 28, the toner image transferred onto the continuous paper P by the secondary transfer device 46 is heated and pressed to perform a fixing process.

  As shown in FIGS. 1 and 3, in this embodiment, the angle change is performed on the downstream side in the transport direction of the continuous paper P of the secondary transfer roll 74 of the secondary transfer device 46 and on the upstream side of the fixing device 28. A post roll 110 constituting the mechanism 100 is provided. The angle changing mechanism 100 has a moving device 112 (see FIG. 4) that moves the post roll 110 in the Z direction, which is the vertical direction. As shown in FIG. 4, the moving device 112 (postroll 110 (see FIG. 3)) is controlled by the control device 18.

  The moving device 112 (see FIG. 4) for moving the post roll 110 shown in FIG. 3 in the vertical direction (Z direction) may be any device.

  An example is the moving device 112 shown in FIG. The moving device 112 in FIG. 5 includes an arm 114 and a stepping motor 116. A shaft portion 110A is rotatably supported by the post roll 110 at one end 114A of the arm 114. A shaft portion 116A of a stepping motor 116 is fixed to the other end portion 114B of the arm 114. The stepping motor 116 is controlled by the control device 18. Under the control of the control device 18, the shaft portion 116A of the stepping motor 116 rotates by an angle corresponding to the control. Then, the post roll 110 rotatably supported by the one end 114A of the arm 114 moves in the Z direction by an amount of movement corresponding to the angle.

  As shown in FIG. 3, the continuous paper P is guided by the post roll 110 and conveyed to the fixing device 28. As the post roll 110 moves up and down (Z direction), the wrap angle θ of the continuous paper P onto which the toner image is transferred with respect to the intermediate transfer belt 44 is changed.

  More specifically, the wrap angle θ will be described along the present embodiment. When the backup roll 72 is viewed in the axial direction, the linear portion PA between the secondary transfer roll 74 and the post roll 110 in the continuous paper P, and This is an angle formed by the straight portion 44A between the backup roll 72 and the support roller 26B (see FIG. 1) in the intermediate transfer belt 44. In other words, the angle of the linear portion PA of the continuous paper P with respect to the linear portion 44A of the intermediate transfer belt 44 as viewed in the axial direction of the backup roll 72.

  Details regarding the movement of the post roll 110 by the moving device 112, that is, the control by the control device 18 of the lap angle θ will be described later.

  The operation display unit 19 includes a display button for receiving operation instructions by various programs, a touch panel type display (not shown) for displaying various information, and hardware keys (not shown) such as a numeric keypad and a start button. Has been. Further, the paper type of the continuous paper P is input.

  The control device 18 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a nonvolatile memory, an I / O, and the like. It is connected. The I / O is an interface for the image forming unit 14 and the like and the control device 18 to exchange data with each other.

<Basic operation of image forming apparatus>
Subsequently, a basic image forming operation by the image forming apparatus 10 will be described.

  When the image forming apparatus 10 shown in FIG. 1 receives a request for an image forming operation (printing operation), the six image forming apparatuses (24W1, 24Y, 24M, 24C, 24K, 24W2) 24, the intermediate transfer device 26, the secondary The transfer device 46, the fixing device 28, etc. are started.

  In each image forming device 24, each photoconductor drum 30 is first rotated, and the surface of each photoconductor drum 30 is charged to a predetermined polarity and potential by each charging device 32. Subsequently, each exposure device 34 applies a charge to the surface of each charged photosensitive drum 30.

By irradiating light based on image information, an electrostatic latent image of each color component is formed on the surface of each photosensitive drum 30.

  Subsequently, each developing device 36 applies a corresponding color (W1, Y, M, C, K, etc.) charged to a predetermined polarity to the electrostatic latent image of each color component formed on each photosensitive drum 30. The toner of W2) is supplied and electrostatically attached, and the electrostatic latent image is developed. As a result, the electrostatic latent image of each color component formed on each photosensitive drum 30 appears as a toner image of each color (W1, Y, M, C, K, W2) developed with the corresponding color toner. Imaged.

  Subsequently, when each color toner image formed on the photosensitive drum 30 of each image forming device 24 is conveyed to the primary transfer position, the primary transfer device 38 applies the toner image of each color to the intermediate transfer belt 44 that rotates. On the other hand, the images are superimposed in order and are primarily transferred.

  Further, in each image forming device 24 in which the primary transfer has been completed, the cleaning device 40 removes deposits such as toner remaining on the surface of the photoconductive drum 30 to clean the surface of the photoconductive drum 30. Thereby, each image forming device 24 is in a state where the next image forming operation is performed.

  Subsequently, in the intermediate transfer device 26, the toner image primarily transferred onto the intermediate transfer belt 44 is held and conveyed to the secondary transfer position NT. On the other hand, in the paper feeder 12, the continuous paper P is supplied from the paper feed roll 20 to the secondary transfer position NT along a predetermined conveyance path prior to the image forming operation.

  At the secondary transfer position NT, the toner image on the intermediate transfer belt 44 is secondarily transferred collectively onto the continuous paper P by the secondary transfer device 46. In addition, in the intermediate transfer device 26 that has finished the secondary transfer, a toner such as toner remaining on the surface of the intermediate transfer belt 44 after the secondary transfer is removed by a belt cleaning device (not shown).

  Subsequently, the continuous paper P onto which the toner image has been secondarily transferred is guided by the post roll 110 of the angle changing mechanism 100 and conveyed to the fixing device 28, and the fixing device 28 performs a fixing process on the continuous paper P. The toner image is fixed. Finally, the continuous paper P after the fixing is finished is discharged from the image forming unit 14 and taken up on the storage roll 22 of the storage device 16.

  Through the above operation, a continuous paper P on which a full-color image is formed by combining the toner images of the respective colors is obtained.

<Details about the control of the wrap angle θ>
Next, details of the control of the movement of the post roll 110 by the control device 18 (control of the moving device 112), that is, the control of the wrap angle θ will be described.

[Control by volume resistivity (Ω · cm) of continuous paper P]
When the volume resistivity of the continuous paper P is small, the control device 18 moves the post roll 110 upward so that the wrap angle θ is smaller than when it is large.

  Here, it is known that the volume resistivity of the continuous paper P varies depending on the paper type. Specifically, it has been found that so-called paper mainly composed of fibers of plants and the like has a smaller volume resistance than a film made of synthetic resin. Then, since the paper type of the continuous paper P is input from the operation display unit 19, the control device 18 controls the wrap angle θ (the position of the post roll 110) based on the input paper type information.

  In this embodiment, when the continuous paper P is a paper system having a small volume resistivity, the wrap angle θ is set to 40 °. However, when the continuous paper P is a film system having a large volume resistivity, the wrap angle θ is The control device 18 moves the post roll 110 downward so as to increase by 5 °. The “paper type” and “film type” will be described later.

[Control by the presence or absence of low-charged toner]
When the low-charge toner is included in the toner image, the control device 18 moves the post roll 110 upward so that the wrap angle θ is smaller than when the toner image does not include the low-charge toner.

  The low-charge toner is a toner that contains a material with which the toner has a low resistance and may have a lower charge amount than other toners. In this embodiment, a white color (W) in which titanium oxide is used as a pigment, and a black color (K) in which carbon black is used as a pigment, a yellow color (Y) and a magenta color in which these are not included. This is a low-charged toner that is less charged than (M) and cyan (C).

  Therefore, in this embodiment, when white (W) toner or black (K) toner is included, the control device 18 moves the post roll 110 upward so that the wrap angle θ is reduced. Let

  At that time, the wrap angle θ is made smaller as the ratio of the low-charged toner (white (W) toner or black (K) toner) to the entire toner image increases. Alternatively, the wrap angle θ is reduced as the amount per unit area of the low-charged toner (white color (W) toner or black color (K)) increases.

  Note that the wrap angle θ may be reduced based on only one of the ratio and the amount per unit area, or the wrap angle θ may be reduced in consideration of both. Considering both, for example, the wrap angle θ is first changed by the ratio, and then the wrap angle θ is decreased as the amount per unit area increases. That is, even if the ratio is the same, the larger the amount per unit area is, the smaller the wrap angle θ is.

  The “ratio of low-charged toner in the toner image” refers to low-charged toner with respect to the entire toner image composed of low-charged toner and non-low-charged toner (or composed of only one of low-charged toner and non-low-charged toner). The mass ratio or volume ratio. The “amount per unit area” is a mass per unit area or a volume per unit area of the low-charge toner in the toner image.

  Titanium oxide lowers the toner charge more than carbon black. That is, the white (W) toner may be charged lower than the black (K) toner.

  Therefore, when white (W) toner is included, the control device 18 decreases the wrap angle θ. At this time, the larger the ratio of white (W) toner to the entire toner image, the smaller the wrap angle θ. Alternatively, the larger the amount per unit area of white (W) toner, the smaller the wrap angle θ. Note that the wrap angle θ may be reduced based on only one of the ratio and the amount per unit area, or the wrap angle θ may be reduced in consideration of both.

  In the present embodiment, the control device 18 has a maximum wrap angle θ of 3 ° when white (W) toner or black (K) toner is included, compared to when it is not included. Make it smaller.

  The control device 18 also includes at least one of the ratio of the low-charged toner, the amount of the low-charged toner per unit area, the ratio of the white (W) toner, and the amount of the white (W) toner per unit area. Accordingly, the wrap angle θ is appropriately changed within a range of 3 ° or less.

  Note that the ratio of the low-charged toner and the amount per unit area, and the ratio of the white color (W) toner and the amount per unit area are appropriately calculated by the control device 18 from information such as image data.

[Control by cumulative image formation time]
The control device 18 moves the post roll 110 upward in order to reduce the wrap angle θ as the cumulative image formation time becomes longer. In the present embodiment, the initial value is reduced by 3 ° at the maximum according to the cumulative image formation time. For example, the wrap angle θ may be gradually decreased gradually, or may be decreased by a predetermined angle for every predetermined time.

[Summary]
As described above, in this embodiment, the reference wrap angle θ is 40 °, but the volume resistivity (paper type) of the continuous paper P and the white color (W) toner or the black color (K). In accordance with the presence / absence / ratio of toner, the amount per unit area, and the accumulated image formation time, the control device 18 moves the post roll 110 up and down as appropriate to change the wrap angle.

<Action and effect>
Next, the operation and effect of this embodiment will be described.

  First, the relationship between the wrap angle θ between the continuous paper P onto which the toner image has been transferred and the intermediate transfer belt 44 and the transfer efficiency and image defects in the secondary transfer will be described.

  FIG. 6 is a graph showing the relationship between the wrap angle θ of each color toner of yellow (Y), magenta (M), and cyan (C) and the transfer efficiency. As can be seen from this graph, as the wrap angle θ decreases, the transfer efficiency improves.

  The table of FIG. 7 shows the relationship between the wrap angle θ and the image defect depending on the paper type of the continuous paper P, specifically, the relationship between the wrap angle θ and the image defect in the paper system and the film system. The image defect is a phenomenon in which when the continuous paper P comes close to the intermediate transfer belt 44, a voltage leak occurs between the two, and a toner image is skipped and a white spot is generated. Since the continuous paper P having a high volume resistivity is highly charged by secondary transfer, voltage leakage is likely to occur between the two, and image defects are likely to occur.

  As can be seen from the table in FIG. 7, the paper-based continuous paper P having a low volume resistivity has substantially no image defect even when the wrap angle θ is 32.5 ° (“◯ (OK)” in the table). However, an image defect occurs in the film-type continuous paper P having a high volume resistivity (described as “× (NG)” in the table).

  Here, a paper system and a film system in the continuous paper P will be described.

  Paper is mainly composed of fibers of plants and the like, and film is composed mainly of synthetic resin. “Paper-based” includes so-called paper such as high-quality paper and medium-quality paper, as well as coated paper and the like having a smooth surface by applying a paint mixed with a white pigment and an adhesive on the surface. The “film system” includes, in addition to a film containing a synthetic resin as a main component, synthetic paper in which a film is coated on paper.

  The labels HG and N cast in the table shown in FIG. 8 are high-quality paper and coated paper, and are paper-based. Moreover, PET50 and YUPO80 in the same table are a film based on PET and a synthetic paper mainly composed of PP and PP. The volume resistivity of the paper system is about 10 12 (Ω · cm), and the film system is about 10 15 (Ω · cm), with a difference of about 3 digits.

  In the present embodiment, the paper-type continuous paper P having a small volume resistivity of about 12th power (Ω · cm) has a wrap angle θ set to 40 °, but is about 10 12 (Ω · cm). In the film-type continuous paper P having a large volume resistivity, the control device 18 moves the post roll 110 downward so that the wrap angle θ is increased by 5 °.

  Therefore, compared with the case where the wrap angle θ of the continuous paper P with respect to the intermediate transfer belt 44 is fixed, the occurrence of image defects is suppressed even when the continuous paper P is changed from the paper system to the film system. Further, as compared with the case where the wrap angle θ is fixed to an angle at which image defects are suppressed in a film system, a decrease in transfer efficiency when the continuous paper P is a paper system is suppressed.

  The continuous paper P having a low volume resistivity does not cause image defects even when the wrap angle θ is 32.5 °, and the continuous paper P having a high volume resistivity has a wrap angle θ of 37. No image defects occur even at 5 °. However, in the present embodiment, in consideration of various variations and margins (margins), the wrap angle θ is set to 40 ° for the paper-based continuous paper P having a small volume resistivity, and the film-based film having a large volume resistivity is used. In the continuous paper P, the wrap angle θ is set to be 5 ° larger.

  Next, the relationship between low-charge toner and transfer efficiency in secondary transfer will be described.

  In white (W) toner and black (K) toner using titanium oxide and carbon black as pigments, if the pigment is unevenly distributed in the vicinity of the surface of the toner base material, the charge exchange between the toners increases, It is easy to generate low-charge toner due to friction. In addition, it is known that low-charge toner causes a decrease in transfer efficiency.

  Therefore, in this embodiment, when white (W) toner or black (K) toner is included, the control device 18 sets the wrap angle θ to 3 ° at the maximum compared to when it is not included. Reduce the transfer efficiency to prevent the transfer efficiency from decreasing. Further, in the present embodiment, the control device 18 includes the ratio of the low charge toner, the amount per unit area of the low charge toner, the ratio of the white color (W) toner, and the unit area of the white color (W) toner. The wrap angle θ is appropriately changed within a range of 3 ° according to at least one of the hit amounts.

  Note that the wrap angle θ is increased by 5 ° in the film-type continuous paper P having a large volume resistivity, but is decreased by 3 ° at the maximum. Further, even if it is reduced by 3 ° at the maximum, it is 42 ° and is larger than 37.5 ° (an example of a predetermined angle), so that image defects are prevented. In this way, compared with the case where the wrap angle θ of the continuous paper P with respect to the intermediate transfer belt 44 is fixed, even if low-charged toner is included, the occurrence of image defects is suppressed and the transfer efficiency is prevented from being lowered. The

  Next, the relationship between the accumulated image formation time and the transfer efficiency in the secondary transfer will be described.

  It has been found that the transfer efficiency in the secondary transfer gradually decreases due to a decrease in the surface releasability of the intermediate transfer belt 44 and the like.

  The graph of FIG. 9 shows the relationship between the number of printed sheets and the transfer efficiency in the secondary transfer. Note that the number of printed sheets is the number obtained by converting the accumulated image formation time to A4 paper. As can be seen from the graph of FIG. 9, the transfer efficiency in the secondary transfer decreases as the number of printed sheets increases (that is, the cumulative image formation time) increases.

  In the present embodiment, the control device 18 suppresses a decrease in transfer efficiency by reducing the maximum by 3 ° according to the accumulated image formation time.

  In addition, in the film type continuous paper P having a large volume resistivity, the wrap angle θ is increased by 5 °, but is decreased by 3 ° at the maximum. Further, even if it is reduced by 3 ° at the maximum, it is 42 °, and since it is larger than 37.5 °, an image defect is prevented.

  Even when low-charged toner is included, even if the wrap angle θ is further reduced by 3 ° from 42 °, it is 39 ° and is larger than 37.5 °, so that image defects are prevented. In this way, compared to the case where the wrap angle θ of the continuous paper P with respect to the intermediate transfer belt 44 is fixed, even if the cumulative image formation time becomes longer, the occurrence of image defects is suppressed and the transfer efficiency is prevented from being lowered. Is done.

  The wrap angle θ and the predetermined angle are examples, and are not limited thereto. What is necessary is just to set suitably according to a structure, specification, etc. of an image forming apparatus.

<Others>
In addition, this invention is not limited to the said embodiment.

  For example, in the present embodiment, the volume resistivity (paper type) of the continuous paper P, the presence / absence / ratio of white (W) toner or black (K) toner, the amount per unit area, and cumulative image formation. Although control device 18 changed lap angle theta according to time, it is not limited to this. For example, the wrap angle θ may be changed by operating the control device 18 (instructing the control device 18) while confirming an image formed by the image forming device 10.

  Depending on at least one of the volume resistivity (paper type) of the continuous paper P, the presence / absence / ratio of white (W) toner or black (K) toner, the amount per unit area, and the cumulative image formation time Thus, the control device 18 may change the wrap angle θ.

  Furthermore, transfer efficiency other than the volume resistivity (paper type) of the continuous paper P, the presence / absence / ratio of white (W) toner or black (K) toner, the amount per unit area, and the cumulative image formation time. The control device 18 may change the wrap angle θ based on the affecting condition.

  Further, for example, in the above embodiment, the toner containing titanium oxide is a white (W) toner using titanium oxide as a pigment, but is not limited thereto. For example, it may be a gold toner or silver toner using titanium oxide as a pigment, or a toner using titanium oxide as an external additive.

  Further, the volume resistivity of the continuous paper P is determined based on the paper type information, but is not limited thereto. For example, a measuring instrument for measuring the volume resistivity of the continuous paper P may be provided, and the wrap angle θ may be changed according to the measurement result.

  Further, the continuous paper P is guided by the post roll 110 of the angle changing mechanism 100 and the wrap angle θ is adjusted, but the present invention is not limited to this. For example, the continuous paper P may be guided by a plate-shaped guide plate, and the wrap angle θ may be changed.

  Moreover, in the said embodiment, although the continuous paper P was used, it is not limited to this. The present invention can also be applied to an image forming apparatus using cut paper.

  The configuration of the image forming apparatus is not limited to the configuration of the above-described embodiment, and various configurations can be employed.

  Furthermore, it cannot be overemphasized that it can implement with a various aspect in the range which does not deviate from the summary of this invention.

10 image forming apparatus 18 control device (an example of angle changing means)
30 photoconductor (an example of an image carrier)
44 Intermediate transfer belt 74 Secondary transfer roll (an example of transfer means)
100 Angle changing mechanism (an example of angle changing means)

Claims (10)

An endless intermediate transfer belt onto which the toner image formed on the image carrier is transferred;
Transfer means for transferring the toner image from the intermediate transfer belt to a recording medium;
An angle changing unit that is provided downstream of the transfer unit in the conveyance direction of the recording medium and changes an angle of the recording medium onto which the toner image is transferred with respect to the intermediate transfer belt;
An image forming apparatus. The angle changing means reduces the angle when the volume resistivity of the recording medium is smaller than when the volume resistivity is large within a range that does not fall below a predetermined angle.
The image forming apparatus according to claim 1. The angle changing means reduces the angle in a case where the toner image contains less low-charged toner than in a case where the toner image does not contain low-charged toner, within a range that does not fall below a predetermined angle;
The image forming apparatus according to claim 1. The angle changing means reduces the angle when the ratio of the low-charged toner in the toner image is larger than when the ratio is small, in a range not less than a predetermined angle;
The image forming apparatus according to claim 3. The angle changing means reduces the angle when the amount per unit area of the low-charged toner in the toner image is larger than a small amount within a range not less than a predetermined angle;
The image forming apparatus according to claim 3 or 4. The angle changing means reduces the angle in a case where the toner image does not contain a toner containing titanium oxide, as long as the angle does not fall below a predetermined angle.
The image forming apparatus according to claim 1. The angle changing means reduces the angle when the ratio of the toner containing titanium oxide in the toner image is larger than when the ratio is small within a range that does not fall below a predetermined angle;
The image forming apparatus according to claim 6. The angle changing means reduces the angle in a case where the amount per unit area of the toner containing titanium oxide in the toner image is larger than that in a case where the amount is smaller than a predetermined angle.
The image forming apparatus according to claim 6 or 7. The toner containing titanium oxide is a white toner.
The image forming apparatus according to claim 6. The angle changing unit reduces the angle when the cumulative image formation time is less than when the accumulated image formation time is small within a range that does not fall below a predetermined angle;
The image forming apparatus according to claim 1.