JP6156719B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a printer, a facsimile machine, and a copying machine.

  In an image forming apparatus, it is important to stably obtain a desired image density. Therefore, in many image forming apparatuses, a density detection pattern made of non-transferred toner that is not transferred onto a sheet is formed on an image carrier. Then, the image density of the density detection pattern is detected by the optical detection means, the image forming conditions are adjusted based on the detection result, and density adjustment control is performed to adjust the toner adhesion amount to be the target amount. Yes.

  In the image forming apparatus described in Japanese Patent Application Laid-Open No. H10-260260, the density is set in the inter-paper area on the intermediate transfer belt, which is an image carrier, corresponding to the interval between the trailing edge of the preceding sheet and the leading edge of the succeeding sheet when performing continuous image formation. A detection pattern is formed, and density adjustment control is performed by detecting the density detection pattern. Further, in this image forming apparatus, in a state where the secondary transfer member and the intermediate transfer belt are in contact with each other, the sheet is conveyed to a secondary transfer region facing the secondary transfer member and the intermediate transfer belt, and an image on the intermediate transfer belt is obtained. Is transferred onto the paper.

  The density detection pattern formed in the inter-paper area on the intermediate transfer belt is formed so as not to contact the paper in the secondary transfer area so as not to stain the paper with the toner constituting the density detection pattern. Therefore, when the density detection pattern passes through the secondary transfer area, there is no paper in the secondary transfer area, so the density detection pattern is the secondary transfer member that faces the intermediate transfer belt in the secondary transfer area. Will be in contact with. As a result, the surface of the secondary transfer member is soiled with the toner constituting the density detection pattern. Therefore, if no measures are taken, the toner adhering to the surface of the secondary transfer member adheres to the back surface of the paper that is subsequently conveyed to the secondary transfer region, and the paper back is soiled.

  The image forming apparatus described in Patent Document 2 includes a cleaning device that cleans the surface of a secondary transfer roller that is a secondary transfer member. This cleaning device has a brush member or a blade member provided in contact with the surface of the secondary transfer roller. Then, the toner adhering to the surface of the secondary transfer roller is scraped off and removed with a brush member or a blade member, thereby suppressing the occurrence of the paper back stain.

  When thick paper is used as the paper, when the paper is transported to the secondary transfer area with the secondary transfer roller and the intermediate transfer belt in contact with each other, there is an impact when the secondary transfer roller and the paper collide. It becomes larger than when thin paper is used. A large vibration is generated in the secondary transfer roller due to the impact, and the vibration is transmitted to the photosensitive member and the exposure device of the image forming unit, so that the writing position of the latent image on the photosensitive member by the exposure device is shifted from the normal position. There is a risk of image defects.

  The inventor of the present application has conducted earnest research, and by using a foam roller provided with a foam around the core as a secondary transfer roller, the impact when the foam roller and the paper collide is alleviated by the foam and the impact It was found that the vibration was reduced and the occurrence of the image defect was suppressed.

  However, the surface of the foaming roller has a plurality of holes, and it is difficult to physically remove the toner that has entered into the holes with a brush or a blade. Therefore, even if the surface of the foaming roller is soiled with the toner constituting the density detection pattern, the toner cannot be sufficiently removed from the surface of the foaming roller by the brush member or blade member of the cleaning device, and the paper back surface is soiled.

  Further, in the above description, the description has been given with respect to the back side of the paper when the density detection pattern is formed in the inter-paper area on the intermediate transfer belt for the purpose of density adjustment control. It is not limited to the detection pattern. An example of attaching the non-transfer toner to the inter-paper area on the image carrier is to replace the deteriorated toner in the developing device with a new toner, and to replace the toner in the developing apparatus in the inter-paper area on the image carrier. Forcibly discharging. Even in this case, the same problem as described above occurs.

  The present invention has been made in view of the above problems, and its object is to adhere to the inter-paper area on the image carrier while suppressing the occurrence of image defects due to vibration caused by the collision between the transfer member and the paper. It is an object of the present invention to provide an image forming apparatus capable of suppressing the occurrence of stains on the back of a sheet due to the non-transferred toner.

In order to achieve the above object, the invention of claim 1 is directed to an image carrier that is rotatably provided and carries a toner image on a surface thereof, a transfer member that is disposed to face the image carrier, and the image carrier. An image provided with non-transfer toner adhering means for adhering non-transfer toner that is not transferred to paper to an inter-paper region existing on the image carrier during a continuous image forming period in which images are continuously formed on the body. In the forming apparatus, the transfer member is a foaming roller, and has contact / separation means for contacting and separating the foaming roller and the image carrier, and there is no margin at the edge or any edge of the entire circumference of the sheet. A special mode for performing borderless printing for forming a toner image up to the edge of the paper and a normal mode for performing bordered printing for forming a toner image so that there is a margin on the entire periphery of the paper, wherein when the special mode, the image carrier times Accordingly, when the inter-paper region existing on the image carrier passes through a transfer region where the image carrier and the transfer member face each other, the contact / separation means causes the image carrier and the transfer member to In the normal mode, the contact / separation operation is performed in the normal mode without performing the contact / separation operation .

In the present invention, by using a foam roller as a transfer member, vibration due to impact when the transfer member and the paper collide is reduced as described above, and an image caused by vibration caused by the collision between the transfer member and the paper is obtained. It is possible to suppress the occurrence of defects.
Also, in the special mode for borderless printing, the image that protrudes from the paper adheres to the transfer member. Therefore, even if the transfer member and the image carrier are separated in the inter-paper area on the image carrier, The member becomes dirty with toner. Therefore, the transfer member and the image carrier are not separated from each other in the inter-paper region, and the toner is reattached to the image carrier from the surface of the transfer member in the inter-paper region, and the toner attached to the surface of the transfer member is removed. Thus, it is possible to suppress the occurrence of stains on the back side of the paper.

  As described above, according to the present invention, the back side of the paper is stained by the non-transfer toner adhered to the inter-paper area on the image carrier while suppressing the occurrence of an abnormal image due to the vibration caused by the collision between the transfer member and the paper. There is an excellent effect that can be suppressed.

FIG. 4 is an explanatory diagram illustrating control details of a contact / separation operation of a secondary transfer roller in bordered printing in the first exemplary embodiment. 1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment. 4 is an enlarged view of four image forming units and their vicinity. FIG. FIG. 4 is a diagram illustrating a state in which a toner pattern for density adjustment control is formed on an intermediate transfer belt. FIG. 6 is a diagram for describing toner density control using a toner pattern. (A) The figure which shows printing with a border, (b) The figure which shows printing without a border, (c) The figure which shows printing without a trailing edge. (A) Schematic diagram showing when the secondary transfer roller and the intermediate transfer belt are in contact, (b) Schematic diagram showing when the secondary transfer roller and the intermediate transfer belt are in a separated state. The graph which shows the result of having evaluated shock jitter. (A) The figure which shows the state which the secondary transfer roller and the intermediate transfer belt have contact | abutted, (b) The state which the secondary transfer roller and the intermediate transfer belt have separated in the space | interval area | region at the time of continuous printing. FIG. 4C is a diagram illustrating a state in which the secondary transfer roller and the intermediate transfer belt are separated from each other during normal separation. (A) The figure which shows the state which the secondary transfer roller and the intermediate transfer belt have contact | abutted, (b) The state which the secondary transfer roller and the intermediate transfer belt have separated in the space | interval area | region at the time of continuous printing. FIG. 4C is a diagram illustrating a state in which the secondary transfer roller and the intermediate transfer belt are separated from each other during normal separation. 10 is a flowchart of secondary transfer contact / separation control in an inter-paper area. FIG. 10 is an explanatory diagram illustrating control contents of secondary transfer contact / separation operation and secondary transfer bias switching control in Embodiment 3. Explanatory drawing which shows the control content of the secondary transfer contact / separation operation | movement and secondary transfer bias switching control in a comparative example. FIG. 10 is an explanatory diagram illustrating control details of secondary transfer contact / separation operation and secondary transfer bias switching control according to the fourth exemplary embodiment. FIG. 10 is an explanatory diagram illustrating control details of secondary transfer contact / separation operation and secondary transfer bias switching control according to the fifth exemplary embodiment. 10 is a flowchart of secondary transfer contact / separation control and secondary transfer bias switching control in Embodiment 6. Explanatory drawing which shows the control content of secondary transfer contact / separation operation | movement and secondary transfer bias switching control in case the printing without trailing edge in Example 6 is set. 10 is a flowchart of secondary transfer contact / separation control and secondary transfer bias switching control in Embodiment 7. FIG. 10 is an explanatory diagram illustrating control contents of secondary transfer contact / separation operation and secondary transfer bias switching control in a case where printing without a trailing edge in Example 7 is set.

Embodiments of the present invention will be specifically described below with reference to the drawings.
FIG. 2 is an overall configuration diagram showing the image forming apparatus according to the embodiment. Here, as an example, a color copying machine (hereinafter referred to as a copying machine) is shown. This color copying machine is an tandem type electrophotographic apparatus by an intermediate transfer method using an intermediate transfer belt 10 as an image carrier. A paper feed table 2 is provided at the bottom of the copier, a copier body 1 is provided above it, and a scanner 3 and an automatic document feeder (ADF) 4 are provided above it.

  The copying machine main body 1 is provided with a transfer device 20 provided with an endless intermediate transfer belt 10 at substantially the center, and the intermediate transfer belt 10 is stretched by a driving roller 14 and driven rollers 15 and 16 in the drawing. Rotate clockwise (surface movement). An intermediate transfer belt cleaning device 17 is provided on the left side of the driven roller 15. The intermediate transfer belt cleaning device 17 removes residual toner remaining on the surface of the intermediate transfer belt 10 after image transfer. Prepared for image formation.

  Above the linear portion of the intermediate transfer belt 10 spanned between the driving roller 14 and the driven roller 15, there are four yellow, magenta, cyan, and black along the surface movement direction of the intermediate transfer belt 10. Image forming units 18Y, 18M, 18C, and 18K are provided.

  FIG. 3 shows an enlarged view of the four image forming units 18Y, 18M, 18C, and 18K and the vicinity thereof. Each of the image forming units 18Y, 18M, 18C, and 18K has drum-shaped photosensitive members 40Y, 40M, 40C, and 40K as latent image carriers (hereinafter, in the case of color coding, Y, M, C, and K, which are color coding codes). Is omitted). Each photoconductor 40 is provided so as to be rotatable in the counterclockwise direction in the drawing. Around the periphery, a charging device 60, a developing device 61, a primary transfer device 62 constituting a primary transfer means, and a photoconductor cleaning device are provided. A device 63 and a charge removal device 64 are provided. Further, as shown in FIG. 2, an exposure device 21 is provided above the photoreceptor 40.

  Below the intermediate transfer belt 10, a secondary transfer roller 22 is provided as a transfer member constituting a secondary transfer unit. The secondary transfer roller 22 is in pressure contact with the driven roller 16 via the intermediate transfer belt 10. Then, the toner images on the intermediate transfer belt 10 are collectively transferred onto the sheet P fed to the secondary transfer region where the secondary transfer roller 22 and the intermediate transfer belt 10 face each other. A transfer bias is applied to the driven roller 16 to form a transfer electric field for transferring the toner image on the intermediate transfer belt 10 to the paper side in the secondary transfer region. Applied by power supply 90.

  In addition, the transfer of the toner image from the intermediate transfer belt 10 to the paper by applying a bias includes a method in which a bias having the same polarity as the normal charging polarity of the toner is applied to the driven roller 16 from the back side of the intermediate transfer belt 10. Further, there is a method in which a bias having a polarity opposite to that of toner is applied to the secondary transfer roller 22 from the back side of the sheet by the secondary transfer bias application power source 90. The bias application method is not limited to either. In this embodiment, a negative bias having the same polarity as the negative polarity, which is the normal charging polarity of the toner, is applied to the driven roller 16 by the secondary transfer bias application power supply 90. .

  In this embodiment, as will be described in detail later, a foaming roller is used as the secondary transfer roller 22. When the thick paper that is the specific paper P is used, when the thick paper is conveyed to the secondary transfer area in a state where the secondary transfer roller 22 and the intermediate transfer belt 10 are in contact with each other, the secondary transfer roller 22 and the thick paper The impact at the time of collision becomes greater than when thin paper is used. A large vibration is generated in the secondary transfer roller 22 due to the impact, and the vibration is transmitted to the photoconductor 40 and the exposure device 21 of the image forming unit 18, and the writing position of the latent image on the photoconductor 40 by the exposure device 21. May deviate from the normal position and image defects may occur.

  Therefore, by using a foam roller provided with a foam around the core as the secondary transfer roller 22, the impact when the foam roller and the cardboard collide is alleviated by the foam, and the vibration due to the impact is reduced. The occurrence of image defects can be suppressed.

  Further, when an image is formed on a thick paper that is a specific paper P, a secondary transfer contact / separation mechanism 70 (see FIG. 7 or the like) described later is used before the leading edge of the thick paper enters the secondary transfer area. It is desirable that the transfer roller 22 and the intermediate transfer belt 10 be separated from each other.

  When a stiff paper P such as thick paper enters the secondary transfer area where the secondary transfer roller 22 and the intermediate transfer belt 10 are in contact with each other, the leading edge of the paper enters the secondary transfer area at the entrance of the secondary transfer area. The vibration when colliding with the next transfer roller 22 or the intermediate transfer belt 10 increases. This vibration may be transmitted to the intermediate transfer belt 10 to cause image quality degradation.

  Therefore, by separating the secondary transfer roller 22 and the intermediate transfer belt 10 when the thick paper enters the secondary transfer area, the leading edge of the thick paper is at the entrance of the secondary transfer area and the secondary transfer roller 22 and the intermediate transfer belt. 10 becomes difficult to collide. Accordingly, it is possible to suppress the occurrence of image quality deterioration due to the vibration caused by the collision being transmitted to the intermediate transfer belt 10.

  Further, even when the secondary transfer roller 22 and the intermediate transfer belt 10 are separated from each other as described above, there is a possibility that the leading end of the thick paper collides with the secondary transfer roller 22 due to variations in the transport path of the thick paper. However, even if the leading edge of the cardboard collides with the secondary transfer roller 22 in this way, by using a foaming roller as the secondary transfer roller 22, the impact at the time of the collision is relieved by the foam, and vibration due to the impact is reduced, The occurrence of the image defect can be suppressed.

  After the leading edge of the thick paper enters the secondary transfer area, the secondary transfer roller 22 and the intermediate transfer belt 10 are brought into contact with each other so that the image formed on the intermediate transfer belt 10 can be transferred onto the thick paper. To.

  In the present embodiment, the secondary transfer roller 22 is rotationally driven by a drive mechanism different from the drive mechanism of the drive roller 14 that rotates the intermediate transfer belt 10. Accordingly, when the thick paper as the paper P enters the transfer nip, the drive from the drive source provided in the drive mechanism of the secondary transfer roller 22 assists the rotational drive of the intermediate transfer belt 10, so that the intermediate transfer belt 10 is driven. 10 speed fluctuations can be reduced. Therefore, shock jitter associated with speed fluctuations of the intermediate transfer belt 10 can be reduced.

  On the downstream side of the secondary transfer roller 22 in the paper conveyance direction, a toner image formed on the paper is fixed by heat and pressure in a fixing nip formed by pressing a pressure roller 27 to an endless fixing belt 26. A fixing device 25 is provided. The sheet after the image transfer is conveyed to the fixing nip of the fixing device 25 by the endless conveying belt 24 that is stretched between the stretching roller 23a and the stretching roller 23b.

  Below the secondary transfer roller 22, a paper reversing device 28 is provided for reversing the front and back of the paper when images are formed on both sides of the paper.

  When making a color copy with the color copying machine of this embodiment, a document is set on the document table 30 of the automatic document feeder 4 or the automatic document feeder 4 is opened and the contact glass 32 of the scanner 3 is opened. Load the original on. When a document is set on the contact glass 32, the document is pressed against the contact glass 32 by closing the automatic document feeder 4. When a start switch (not shown) is pressed, the original is automatically fed onto the contact glass 32 when the original is set on the automatic document feeder 4.

  On the other hand, when a document is set on the contact glass 32, the scanner 3 immediately operates and the first traveling body 33 and the second traveling body 34 start traveling. Thereby, light from the light source of the first traveling body 33 is emitted toward the document, and reflected light from the document surface is reflected by the mirror of the first traveling body 33 toward the second traveling body 34. Further, the direction of 180 degrees is changed by the pair of mirrors of the second traveling body 34, passes through the imaging lens 35, enters the reading sensor 36, and the contents of the document are read.

  Further, by pressing the start switch described above, the intermediate transfer belt 10 starts rotating, and at the same time, each photosensitive member 40 also starts rotating, and each single color of yellow, magenta, cyan, and black is set on each photosensitive member 40. A toner image is formed. Each single-color toner image formed on each photoconductor 40 in this way is superimposed and sequentially transferred onto the intermediate transfer belt 10 that rotates in the clockwise direction in the drawing to form a full-color composite color image. .

  On the other hand, the paper feed roller 42 of the selected paper feed stage in the paper feed table 2 rotates and the paper P is fed out from the selected paper feed cassette 44 in the paper bank 43 and separated into one sheet by the separation roller 45. And conveyed to the paper feed path 46. The fed paper P is transported to the paper feed path 48 of the copying machine main body 1 by the transport roller 47 and comes into contact with the registration roller pair 49 to temporarily stop. In the case of manual feed, the paper P set on the manual feed tray 51 is fed out by the rotation of the manual feed roller 50, separated into one sheet by the manual separation roller 52, and conveyed to the manual feed path 53. Then, it comes into contact with the registration roller pair 49 and temporarily stops.

  In any case, the registration roller pair 49 starts to rotate at an accurate timing in accordance with the color image on the intermediate transfer belt 10, and the sheet P that has been stopped is transferred between the intermediate transfer belt 10 and the secondary transfer roller 22. Send in between. As a result, a color image is transferred from the intermediate transfer belt 10 onto the sheet by the action of the transfer electric field due to the transfer bias applied to the secondary transfer roller 22. The sheet P on which the color image has been transferred is conveyed to the fixing device 25 by the conveying belt 24, heated and pressed to fix the transferred image, guided to the discharge side by the switching claw 55, and discharged by the discharge roller 56. The paper is discharged onto the paper discharge tray 57 and stacked.

  When the double-sided copy mode is selected, the paper P on which an image is formed on the front surface is conveyed to the paper reversing device 28 side by the switching claw 55, is reversed and guided again to the transfer position, and the image is formed on the back surface. After being formed, the paper is discharged onto a paper discharge tray 57 by a discharge roller 56.

  When a black single color image is formed on the intermediate transfer belt 10, the driven rollers 15 and 16 other than the driving roller 14 are moved so that the yellow, magenta, and cyan photoconductors 40 Y, 40 M, and 40 C are transferred to the intermediate transfer belt 10. It is trying to keep away from. In a so-called 1-drum type image forming apparatus that has only one photoconductor 40 instead of the tandem type as shown in FIG. 2, first, black image formation is performed in order to increase the first copy speed. It is common to do. After that, image formation of the remaining colors is performed only when the document is in color.

The registration roller pair 49 is usually used while being grounded, but a bias can be applied to remove paper dust from the paper P. For example, when a bias is applied using a conductive rubber roller having a diameter of 18 [mm] and a surface coated with a conductive NBR rubber having a thickness of 1 [mm], the voltage may be applied as follows. That is, the volume resistance of the rubber material is about 10 ⁹ [Ω · cm], and a voltage of about −800 [V] is applied to the roller on the toner transfer side (front side) of the registration roller pair 49, and the back side of the paper A voltage of about +200 [V] is applied to the side roller.

  In general, in the intermediate transfer method, paper dust is difficult to move to the photoreceptor 40, so there is little need to consider paper dust transfer, and there is no problem even if it is grounded. Further, although a DC bias is generally applied as the applied voltage, it is also possible to apply an AC voltage having a DC offset component in order to charge the paper more uniformly. The sheet surface after passing through the registration roller pair 49 to which a bias is applied in this way is slightly charged on the minus side. For this reason, in the transfer from the intermediate transfer belt 10 to the paper P, the transfer condition changes compared to the case where no voltage is applied to the registration roller, and the transfer condition may be changed.

  Further, the copying machine of this embodiment is provided with a toner adhesion amount sensor 5 as an adhesion amount detection means for detecting the toner adhesion amount (density) on the intermediate transfer belt 10. The toner adhesion amount sensor 5 used this time is of a type that uses an infrared light emitting diode as a light emitting portion and a photodiode as a diffuse reflection light receiving portion and outputs a voltage corresponding to the amount of received light.

  FIG. 4 shows a state in which a toner pattern TP for density adjustment control composed of a plurality of types of density detection toner patches is formed on the intermediate transfer belt 10. The toner pattern TP formed on the photoconductor 40 is transferred onto the intermediate transfer belt 10 by the primary transfer device 62 in the primary transfer region where the photoconductor 40 and the intermediate transfer belt 10 are in contact with each other. 10 is attached to the top.

  The toner pattern TP for density adjustment control is usually formed with a plurality of toner patches for each color so that the target densities are different from each other, and the toner adhesion amount (toner density) of each toner patch is attached facing the intermediate transfer belt 10. The toner adhesion amount sensor 5 is detected. The toner adhesion amount detection operation by the toner pattern TP is performed at the following two timings. That is, it is performed in a process control mode (density adjustment control mode) different from the image forming operation, or an inter-paper area (between toner images) on the intermediate transfer belt 10 during a continuous image forming period (during continuous printing). Area).

  The toner pattern TP is formed in the inter-sheet area on the same principle as a normal toner image. Specifically, a toner image is formed by the photoreceptor 40, the charging device 60, the developing device 61, and the like shown in FIG.

  The toner density control using this toner pattern TP will be described. The toner adhesion amount of each toner patch of the toner pattern TP is detected by the toner adhesion amount sensor 5 shown in FIG. Based on the detected value, the density adjustment control unit 80 controls one or more of the toner replenishment motor 96, the developing bias applying device 81, the charging bias applying device 82, and executes image density adjustment. When the adjustment is performed by the control of the toner replenishing motor 96, the image density is adjusted by adjusting the toner density by adjusting the toner replenishment by the toner replenishing device 95. When adjusting the developing bias or the charging bias under the control of the developing bias applying device 81 or the charging bias applying device 82, the image density is adjusted by adjusting the bias value. Although FIG. 5 shows only the black image forming unit 18K, the actual control is performed for all colors.

  Further, if the image forming operation with a low image area continues, the amount of old toner that stays in the developing device 61 for a long time increases, so that the toner charging characteristics deteriorate and the image quality deteriorates when used for image formation (deterioration of developing ability). , Transferability decline). For this reason, the copying machine of this embodiment has a refresh mode in which the toner in the developing device 61 is refreshed. In this refresh mode, in order to prevent old toner from staying in the developing device 61, the toner is discharged to the inter-paper area on the photoconductor 40 at a certain timing, and after the toner is discharged, new toner is supplied to the developing device 61 and developed. The toner in the device 61 is refreshed.

  A control unit (not shown) stores the toner consumption amount of each developing device 61Y, 61M, 61C, 61K and the operation time of each developing device 61Y, 61M, 61C, 61K. Then, at each predetermined timing, each developing device 61 is checked whether or not the toner consumption amount is equal to or less than a threshold with respect to the operation time of the developing device 61 for a predetermined period. Then, the refresh mode is executed for the developing device 61 below the threshold.

When the refresh mode is executed, a toner consumption pattern is formed in the inter-sheet area on the photoreceptor 40 and is transferred to the intermediate transfer belt 10. The adhesion amount of the toner consumption pattern is determined based on the toner consumption amount with respect to the operation time of the developing device 61 for a predetermined period, and the maximum adhesion amount per unit area may be about 1.0 [mg / cm ² ]. . Further, when the toner Q / d distribution of the toner consumption pattern transferred to the intermediate transfer belt 10 is measured, it is substantially aligned with the normal charging polarity.

  Further, the toner consumption pattern thus formed in the inter-sheet area on the photoreceptor 40 is transferred to the inter-sheet area of the intermediate transfer belt 10 and removed from the intermediate transfer belt 10 by the intermediate transfer belt cleaning device 17.

  Next, bordered printing and borderless printing will be described. FIG. 6A shows bordered printing, and FIG. 6B shows borderless printing. FIG. 6C shows the trailing edgeless printing.

  In the color copying machine according to the present embodiment, a printing mode with a margin for forming a toner image on the sheet so that there is a margin on the entire periphery of the sheet, and a toner image on the sheet so that no margin is formed on any edge of the sheet. And a borderless printing mode. For example, the operator selects one of the bordered printing mode and the borderless printing mode by using an operation unit (not shown) provided in the copying machine main body 1, and executes bordered printing or borderless printing. .

  In bordered printing, the toner image formed on the intermediate transfer belt 10 is entirely contained in the sheet, and as shown in FIG. 6A, margins (upper margin, lower margin, Left margin, right margin). On the other hand, in borderless printing, a toner image is formed on the intermediate transfer belt 10 so as to protrude from the edge of the paper, and as shown in FIG. There is no margin at the edge of (up, down, left and right). Here, FIG. 6B shows a state in which there is no margin at the edge of the entire circumference (upper, lower, left, and right) of the paper, but in this embodiment, of any of the upper, lower, left, and right edges of the paper, If there is no margin at one or more edges, borderless printing is assumed.

  In the trailing edgeless printing, the intermediate transfer belt 10 is configured such that the toner image protrudes from the lower edge of the sheet and the toner image does not protrude from the other edges (upper edge, left edge, and right edge) of the sheet. A toner image is formed thereon. That is, as shown in FIG. 6C, the toner image exists up to the bottom edge of the sheet, there is no margin (lower margin) at the lower edge of the sheet, and margins (upper margin, left margin, and right margin) are formed at the other edges of the sheet. This is a state where there is a margin.

  Note that the control method of the image forming apparatus related to the image formation of borderless printing is known, and the present invention does not limit the control method of borderless printing.

  Next, an embodiment corresponding to the present invention will be described using the electrophotographic apparatus having the above-described configuration.

[Example 1]
In this embodiment, the secondary transfer roller 22 is a foaming roller in which a foaming rubber as a foaming member is provided around a metallic cored bar member. The material of the foamable rubber is not particularly limited, but here, NBR rubber was used, and the formulation was adjusted so that the Asker C hardness was 40 [°].

  FIG. 7 is a schematic diagram for explaining the configuration and operation of the secondary transfer contact / separation mechanism 70 that separates the secondary transfer roller 22 from the intermediate transfer belt 10. 7A shows the case where the secondary transfer roller 22 and the intermediate transfer belt 10 are in contact with each other, and FIG. 7B shows the case where the secondary transfer roller 22 and the intermediate transfer belt 10 are in contact with each other. This is when it is in a separated state.

  The secondary transfer contact / separation mechanism 70 of this embodiment supports the secondary transfer roller shaft 22a of the secondary transfer roller 22 so as to be rotatable, and swings that can swing with respect to the apparatus main body about the swing shaft 29. A member 19 is provided. In addition, the cam member has a contact / separation cam 71 as a cam member that can be rotated around a rotation shaft 71a and is arranged so that the cam surface contacts the cam contact position S provided on the lower surface of the swing member 19. ing. Furthermore, a drive device (contact / separation motor) (not shown) is provided as a rotation drive means for rotating the contact / separation cam 71.

  In this embodiment, the contact / separation cam 71 is rotated to a rotation position where the cam surface portion of the contact / separation cam 71 farthest from the rotation shaft 71 a contacts the cam contact position S of the swing member 19. In this state, as shown in FIG. 7A, the secondary transfer roller 22 and the intermediate transfer belt 10 are in contact with each other. Further, in the state in which the contact / separation cam 71 is rotated to the rotation position where the cam surface portion closest to the rotation shaft 71a of the contact / separation cam 71 is in contact with the cam contact position S of the swing member 19, FIG. As shown in (b), the secondary transfer roller 22 and the intermediate transfer belt 10 are separated from each other. The rotation position where the cam surface portion closest to the rotation shaft 71a of the contact / separation cam 71 is in contact with the cam contact position S of the swinging member 19 is 180 from the rotation position of FIG. It is a position rotated by degrees.

  When the contact / separation cam 71 is rotated from the contact state, the swinging member 19 is kept in contact with the cam surface of the contact / separation cam 71 by its own weight. Therefore, when the contact / separation cam 71 is rotated from the contact state, the swinging member 19 rotates around the swinging shaft 29 in the clockwise direction in the drawing, and the secondary transfer roller 22 is interlocked with the rotation of the secondary transfer roller 22 in FIG. As shown in FIG. 2, the intermediate transfer belt 10 is separated.

  In this embodiment, when the inter-sheet area on the intermediate transfer belt 10 passes through the secondary transfer area, the secondary transfer roller 22 is separated from the intermediate transfer belt 10 by the secondary transfer contact / separation mechanism 70. Then, before the next sheet P enters the secondary transfer region, the secondary transfer roller 22 is brought into contact with the intermediate transfer belt 10 by the secondary transfer contact / separation mechanism 70.

  FIG. 1 is an explanatory diagram showing the control content of the contact / separation operation of the secondary transfer roller 22 in bordered printing in this embodiment. In FIG. 1, the horizontal axis represents time, and the timing at which the paper P, the toner image, and the toner pattern TP pass through the secondary transfer region and the contact / separation timing of the secondary transfer roller 22 are shown.

  In this embodiment, a toner pattern TP is formed in the inter-paper area on the intermediate transfer belt 10 at a predetermined timing during continuous printing, and this is detected by the toner adhesion amount sensor 5 to perform process control (density adjustment control). Run. At this time, when the toner pattern TP formed on the intermediate transfer belt 10 passes through the secondary transfer area, the sheet P does not exist in the secondary transfer area. Therefore, if the secondary transfer roller 22 remains in contact with the intermediate transfer belt 10, the toner pattern TP contacts and adheres to the surface of the secondary transfer roller 22. Then, the toner adhering to the surface of the secondary transfer roller 22 is transferred from the secondary transfer roller 22 onto a sheet that is subsequently conveyed to the secondary transfer region, and the back of the sheet is stained.

  Therefore, in this embodiment, the contact / separation control as shown in FIG. 1 is performed by controlling the contact / separation motor of the contact / separation cam 71 by a control unit (not shown). Then, during the toner pattern passage period (non-transfer toner passage period) in which the toner pattern TP passes through the secondary transfer region, the secondary transfer roller 22 and the intermediate transfer belt 10 are separated from each other.

  Specifically, first, as shown in FIG. 7A, the secondary transfer roller 22 and the intermediate transfer belt 10 are brought into contact with each other, and the toner image immediately before the formation of the toner pattern TP in the secondary transfer region is transferred to the preceding paper P1. Secondary transfer to. After that, after the trailing edge of the preceding sheet P1 passes through the secondary transfer area, the control unit controls the contact / separation motor of the contact / separation cam 71 to start the rotation of the contact / separation cam 71 (time A in FIG. 1). ). The rotation start timing of the contact / separation cam 71 at this time is set as follows. That is, before the leading edge of the toner pattern TP enters the secondary transfer region, the half rotation of the contact / separation cam 71 is completed, and the secondary transfer roller 22 and the intermediate transfer belt 10 are as shown in FIG. It is set so as to be in a separate state (time B in FIG. 1).

  Thereafter, after the trailing end of the toner pattern TP has passed through the secondary transfer region, the control unit controls the contact / separation motor of the contact / separation cam 71 to start rotation of the contact / separation cam 71 (time in FIG. 1). C). The rotation start timing of the contact / separation cam 71 at this time is set as follows. That is, before the leading edge of the trailing sheet P2 enters the secondary transfer region, the half rotation of the contact / separation cam 71 is completed, and the secondary transfer roller 22 and the intermediate transfer belt 10 are shown in FIG. Such a contact state is set (time D in FIG. 1).

FIG. 8 shows the result of evaluation of shock jitter in this configuration. Evaluation was performed by visual rank evaluation of 5 steps. Rank 5 is the best evaluation without jitter, rank 1 is the worst, and acceptable is rank 4 or higher. The evaluation paper is a thick paper with a basis weight of 300 [g / m ² ], and in order to evaluate the influence on the primary transfer, development, and writing at the time of entering the paper, the worst jitter generated when 10 consecutive evaluation papers are passed is used. evaluated.

  As the secondary transfer roller 22, in addition to the foaming roller having an Asker C hardness of 40 [°] in the embodiment, for comparison, foaming having an Asker C hardness of 70 [°], 60 [°], 50 [°], and 30 [°] is used. Evaluation was also made using a roller and an 80 [°] solid rubber roller.

  From FIG. 8, it can be seen that as the hardness of the secondary transfer roller 22 is lower, jitter is less likely to occur, and if the Asker C hardness is 60 [°] or less, it is within the allowable range. Furthermore, if the Asker C hardness is 40 [°] or less, the jitter will be improved to be invisible. However, it is not desirable to lower the roller hardness more than necessary, because the lower the roller hardness, the easier it is to deform by repeatedly applying pressure.

[Example 2]
The second embodiment is an example in which a secondary transfer contact / separation mechanism for more reliably moving the secondary transfer roller 22 is mounted. Schematic diagrams of the secondary transfer contact / separation mechanism are shown in FIGS.

  The secondary transfer contact / separation mechanism 70 of the present embodiment has two or more different separation distances between the secondary transfer roller 22 and the intermediate transfer belt 10 when the secondary transfer roller 22 and the intermediate transfer belt 10 are separated from each other. The separating operation is performed. That is, the secondary transfer roller 22 and the intermediate transfer belt 10 are separated from each other even during normal separation, which is during separation other than the above-described inter-paper region during continuous printing.

  The secondary transfer contact / separation mechanism 70 shown in FIG. 9 supports the secondary transfer roller shaft 22a of the secondary transfer roller 22 so as to be rotatable, and can swing with respect to the apparatus main body about the swing shaft 29. A member 19 is provided. Further, the cam member has a contact / separation cam 72 as a cam member that is rotatable about a rotation shaft 72a and is arranged so that the cam surface contacts the cam contact position S provided on the lower surface of the swing member 19. ing. Furthermore, a drive device (contact / separation motor) (not shown) is provided as a rotational drive means for rotating the contact / separation cam 72.

  The secondary transfer contact / separation mechanism 70 shown in FIG. 9 is a configuration example in which the secondary transfer roller 22 can be moved relative to the intermediate transfer belt 10 in three stages by the shape of the contact / separation cam 72. FIG. 9A shows a state where the secondary transfer roller 22 and the intermediate transfer belt 10 are in contact with each other. FIG. 9B shows a state in which the secondary transfer roller 22 and the intermediate transfer belt 10 are separated from each other in the inter-paper area during continuous printing. FIG. 9C shows a state in which the secondary transfer roller 22 and the intermediate transfer belt 10 are separated at the time of the normal separation, and the secondary transfer roller 22 is further moved to the intermediate transfer belt 10 from FIG. 9B. Away from

  In addition, the secondary transfer contact / separation mechanism 70 is operated from any separated state during the contact operation in which the secondary transfer roller 22 and the intermediate transfer belt 10 are shifted from the respective separated states to the contact state by two or more separated operations. It is comprised so that it may transfer to a contact state by one operation | movement. Further, in the separation operation for shifting from the contact state to each separation state, it is configured to shift to any separation state by one operation.

  That is, by rotating the contact / separation cam 72 by a contact / separation motor (not shown), any of the states of FIGS. 9A to 9C can be used. The secondary transfer roller 22 can be moved to different positions in (c).

  In this example, the state shown in FIG. 9B can be obtained by rotating the contact / separation cam 72 by 180 degrees from the state shown in FIG. 9A, and FIG. 9A or FIG. By rotating the contact / separation cam 71 by 90 degrees from this state, the cam shape can be changed to the state shown in FIG. However, the shape of the contact / separation cam 71 is not limited to this.

  FIG. 10 shows a configuration example in which the secondary transfer roller 22 can be moved with respect to the intermediate transfer belt 10 in three stages by using two cams, that is, the contact / separation cam 73 and the contact / separation cam 77. FIG. 10A shows a state where the secondary transfer roller 22 and the intermediate transfer belt 10 are in contact with each other. FIG. 10B shows a state in which the secondary transfer roller 22 and the intermediate transfer belt 10 are separated from each other in the inter-paper area during continuous printing. FIG. 10C shows a state in which the secondary transfer roller 22 and the intermediate transfer belt 10 are separated at the time of the normal separation, and the secondary transfer roller 22 is further moved to the intermediate transfer belt 10 from FIG. Away from

  The secondary transfer contact / separation mechanism 70 shown in FIG. 10 supports the secondary transfer roller shaft 22a of the secondary transfer roller 22 so as to be rotatable, and swings about the swing shaft 29 so as to swing relative to the apparatus main body. The upper end of the spring 76 is attached to the lower right side of the swing member 19 in the figure. In addition, a contact plate 78 provided at the lower end of the spring 76 is provided with a contact / separation cam 77 as a cam member that can be rotated about a rotation shaft 77a and is arranged so that the cam surface contacts the contact plate 78. . The contact / separation cam 77 is rotationally driven by a contact / separation motor (not shown) as a rotational drive means.

  Further, the swing arm 74 is swingable with respect to the apparatus main body about the swing support point 75, the lower surface at the center in the figure is in contact with and away from the secondary transfer roller shaft 22a, and the lower surface on the left side in the figure is rocked. A swing arm 74 that is in contact with and away from the moving shaft 29 is provided. This swing arm 74 is provided with a rotation drive means (not shown) as a cam member that is arranged so that the cam surface comes into contact with a cam contact position provided on the upper left side of the swing arm 74 in the figure. It can be swung by being driven to rotate by the contact / separation motor.

  10A, when the contact / separation cam 73 is rotated by a contact / separation motor (not shown), the swing arm 74 swings downward about the swing support point 75. The secondary transfer roller shaft 22a is pushed down on the lower surface. Further, when the secondary transfer roller shaft 22a is pushed down, the rocking member 19 is also swung down about the rocking shaft 29 and pushed down. As a result, the secondary transfer roller 22 is separated from the intermediate transfer belt 10 as shown in FIG. At this time, the spring 76 is urged by the swing member 19 and contracts more than the state shown in FIG. At this time, the swing member 19 is urged upward by the compression spring 76, but the secondary transfer roller shaft 22 a supported by the swing member 19 comes into contact with the lower surface of the swing arm 72 to swing. The vertical position of the member 19 is positioned at the height shown in FIG.

  Furthermore, since the lower end of the compression spring 76 is lowered by rotating the contact / separation cam 77 180 degrees with a contact / separation motor (not shown) from the state of FIG. The biasing force that biases the member 19 upward decreases. As a result, the upper end of the compression spring 76 is lowered due to the weight of the swinging member 19 and the secondary transfer roller 22 is further intermediate-transferred than the position shown in FIG. 10B, as shown in FIG. It moves away from the belt 10. At this time, the swing member 19 is positioned at a height where the weight of the swing member 19 and the like and the biasing force of the compression spring 76 are balanced. As a result, the separation state in which the separation distance between the secondary transfer roller 22 and the intermediate transfer belt 10 is longer than the separation state illustrated in FIG.

  FIG. 11 shows a flowchart of secondary transfer contact / separation control in the inter-sheet area. This flowchart is an example in which the secondary transfer contact / separation mechanism 70 shown in FIG. 9 is used, but is not limited thereto. The secondary transfer contact / separation mechanism 70 and other contact / separation configurations shown in FIG. 10 are basically the same as long as the secondary transfer roller 22 can be moved relative to the intermediate transfer belt 10 in three stages. .

  First, after the print job is notified (S1), the contact / separation cam 72 is rotated 90 degrees before the paper P is input to the secondary transfer region, and the state shown in FIG. (S2). After the printing operation is performed (S3), when there is no next image to be printed and printing is completed (Y in S4), the contact / separation cam 72 is rotated 90 degrees to change the state from FIG. 9A to FIG. The state is changed to (c) (S9), printing is finished, and a series of control is finished.

  On the other hand, when there is a next image (N in S4), the contact / separation cam 72 is rotated 180 degrees after the trailing edge of the sheet has passed through the secondary transfer area, and the state shown in FIG. ) State (S5). Then, before the next sheet leading edge is input to the secondary transfer area, the contact / separation cam 72 is rotated 180 degrees to change from the state of FIG. 9B to the state of FIG. 9A (S6). After the printing operation (S7), if there is no next image and printing is finished (Y in S8), the contact / separation cam 72 is rotated 90 degrees to change the state of FIG. 9 (a) to FIG. 9 (c). (S9), the printing is finished, and a series of control is finished.

  On the other hand, if there is a next image (N in S8), the contact / separation cam 72 is rotated 180 degrees after the trailing edge of the sheet passes through the secondary transfer region, and the state shown in FIG. ) (S5), and thereafter, the same control as described above is repeated until there is no next image and printing is completed.

[Example 3]
In this embodiment, while the secondary transfer roller 22 is separated from the intermediate transfer belt 10, the secondary transfer bias applied by the secondary transfer bias application power supply 90 is a bias having a polarity opposite to that during normal printing. The configuration is switched to (positive polarity bias). In this embodiment, a bias is applied to the driven roller 16 by the secondary transfer bias application power supply 90.

  At this time, a toner pattern TP for density adjustment control is formed in the inter-paper area on the intermediate transfer belt 10, and the toner pattern TP is attached to the secondary transfer roller 22 by the reverse polarity bias. It was set as the structure which prevents.

  FIG. 12 is an explanatory diagram illustrating the control contents of the secondary transfer contact / separation control and the secondary transfer bias switching control in the inter-sheet area in the present embodiment. In this figure, the horizontal axis is time, and the timing at which the paper P, toner image, and toner pattern TP pass through the secondary transfer region, the contact / separation timing of the secondary transfer roller 22, and the secondary transfer bias application power source 90 The next transfer bias switching timing is shown.

  In this embodiment, the secondary transfer bias is switched by first changing the secondary transfer bias from minus to after the trailing edge of the preceding paper P1 passes through the secondary transfer region between the secondary transfer roller 22 and the intermediate transfer belt 10. (Time A in FIG. 12). When the toner pattern TP is input to the secondary transfer area, the secondary transfer bias is set to be positive (time B in FIG. 12). Next, after the toner pattern TP passes through the secondary transfer region, the secondary transfer bias is switched from plus to minus (time C in FIG. 12). Then, the secondary transfer bias is set to the normal output before the leading edge of the next succeeding paper P2 is input to the secondary transfer area (time D in FIG. 12).

  Next, as a comparative example, when the secondary transfer roller 22 is separated from the intermediate transfer belt 10, the secondary transfer bias is not switched to a reverse polarity bias (plus polarity bias) but the output is turned off. To do. FIG. 13 is an explanatory diagram showing the control contents of the contact / separation operation in the comparative example, where the horizontal axis represents time, the timing at which the paper P, the toner image, and the toner pattern TP pass through the secondary transfer region, and the secondary transfer roller. 22 shows contact timings.

  To switch the secondary transfer bias in the comparative example, first, the secondary transfer bias is turned off (time A in FIG. 13) after the trailing edge of the preceding sheet P1 passes through the secondary transfer area. As a result, when the toner pattern TP is input to the secondary transfer region, the secondary transfer bias may not drop to 0 (time B in FIG. 13). Next, after the toner pattern TP passes through the secondary transfer region, the secondary transfer bias is turned on (time C in FIG. 13). Then, the secondary transfer bias switching is completed before the leading edge of the next succeeding paper P2 is input to the secondary transfer area (time D in FIG. 13).

  When the secondary transfer bias is switched as in the comparative example, depending on the performance of the power supply, the secondary transfer bias is reduced to 0 as compared with the case of switching to the reverse polarity bias as in the present embodiment. Easy to take time. Therefore, as shown at time B in FIG. 13, when the toner pattern TP is input to the secondary transfer region, the secondary transfer bias may not drop to zero. In this case, there is a problem that the toner receives a force in the direction of the secondary transfer roller 22 due to the potential difference between the intermediate transfer belt 10 and the secondary transfer roller 22, and the toner flies to the secondary transfer roller 22 and becomes dirty. Can occur.

  On the other hand, while the secondary transfer roller 22 is separated from the intermediate transfer belt 10 in the inter-sheet area as in this embodiment, the secondary transfer bias is switched to a polarity opposite to the normal polarity. As a result, the force due to the electric field applied to the toner pattern TP on the intermediate transfer belt 10 acts in the direction opposite to that of the secondary transfer roller 22. Therefore, it becomes difficult for toner to fly from the intermediate transfer belt 10 toward the secondary transfer roller 22, and toner contamination on the secondary transfer roller 22 can be suppressed. Also, depending on the power supply performance, it takes some time for the secondary transfer bias to switch to the reverse polarity bias. On the other hand, compared to the case where the secondary transfer bias is turned off as in the comparative example, the potential difference between the secondary transfer roller 22 and the intermediate transfer belt 10 becomes 0 as shown at time B in FIG. Can be fast.

  Here, the secondary transfer bias is generally controlled at a constant current in order to keep the transfer electric field constant even when the resistance of the paper, the secondary transfer roller 22 or the like changes. However, when the secondary transfer bias is switched to the reverse polarity when the secondary transfer roller 22 and the intermediate transfer belt 10 are separated from each other, the secondary transfer roller 22 and the intermediate transfer belt 10 are separated from each other so that the current flows. May be difficult to flow or may not flow. For this reason, when the secondary transfer bias having the reverse polarity applied while the secondary transfer roller 22 and the intermediate transfer belt 10 are separated is controlled at a constant current, the voltage is very high so that a predetermined current flows. Become bigger. As a result, current may leak to another place, disturbing the image, or damaging the apparatus.

  On the other hand, in this embodiment, the secondary transfer bias having a reverse polarity applied while the secondary transfer roller 22 and the intermediate transfer belt 10 are separated is controlled at a constant voltage. As a result, it is possible to suppress problems associated with abnormal voltage increases as described above, and to suppress toner flying from the intermediate transfer belt 10 to the secondary transfer roller 22.

[Example 4]
In the fourth embodiment, when the borderless printing mode, which is a special mode, is selected, the secondary transfer roller 22 is not separated from the intermediate transfer belt 10 in the inter-paper area on the intermediate transfer belt 10, and is not The next transfer bias is switched to a bias having a polarity opposite to that during normal printing. Thus, the toner attached to the secondary transfer roller 22 is retransferred to the intermediate transfer belt 10 in the inter-paper area. In this embodiment, the toner pattern is not formed in the inter-paper area during continuous printing.

  Paper backside contamination that may be caused by toner adhering to the surface of the secondary transfer roller 22 is not only due to the toner pattern TP formed in the inter-paper area on the intermediate transfer belt 10.

  In the borderless printing mode in which printing is performed to the full edge of the paper P, the paper transport position varies to some extent. Therefore, if the image size is exactly the same as the paper size, depending on the accuracy of paper conveyance, the image may be shifted with respect to the paper P, resulting in a white-out portion and a problem that borderless printing will not occur. In order to solve this, generally, an image is formed on the intermediate transfer belt 10 so as to protrude from the edge of the paper P, and the image size is made larger than the paper size.

  However, when an image is formed so as to protrude from the edge of the paper P, the toner that protrudes from the edge of the paper P adheres to the intermediate transfer belt 10. Therefore, when an image is transferred from the intermediate transfer belt 10 to the paper P in the secondary transfer region, the protruding toner adheres to the surface of the secondary transfer roller 22 from the intermediate transfer belt 10. Therefore, the toner adhering to the surface of the secondary transfer roller 22 adheres to the back surface of the paper P that is subsequently conveyed to the secondary transfer region, and the paper back is contaminated by the protruding toner.

  FIG. 14 is an explanatory diagram showing the control contents of the secondary transfer contact / separation control and the secondary transfer bias switching control in the inter-paper region in the present embodiment. This figure shows the switching timing of the secondary transfer bias by the secondary transfer bias application power source 90 in the inter-sheet area on the intermediate transfer belt 10 in this embodiment, with the horizontal axis as time. During normal printing, a negative bias having the same polarity as the negative charging polarity of the toner is applied to the driven roller 16 by the secondary transfer bias applying power supply 90.

  In the present embodiment, the secondary transfer bias is switched by first switching the secondary transfer bias from minus to plus after the trailing edge of the preceding paper P1 passes through the secondary transfer area (time A in FIG. 14). The time T1 for applying the positive bias is set such that the distance D1 when the distance D1 = the rotational speed of the secondary transfer roller 22 × the time T1 is at least longer than the circumference of the secondary transfer roller 22 ( Time between time B and time C in FIG. 14).

  By such a bias switching operation, the negatively charged toner attached to the surface of the secondary transfer roller 22 is retransferred to the intermediate transfer belt 10, and the toner on the surface of the secondary transfer roller 22 is removed. Further, by making the distance D1 longer than the circumference of the secondary transfer roller 22, negatively charged toner on the entire circumference of the secondary transfer roller 22 can be removed.

  Next, the secondary transfer bias is switched from plus to minus after the lapse of time T1, and before the leading edge of the succeeding paper P2 is input to the secondary transfer area, the switching of the secondary transfer bias is completed, and the secondary transfer roller is completed. The toner removal operation 22 is completed (time D in FIG. 14).

  In the borderless printing mode, the toner is reattached from the surface of the secondary transfer roller 22 to the intermediate transfer belt 10 in the inter-paper area, and the toner attached to the surface of the secondary transfer roller 22 is removed, thereby making the paper back stain. Can be suppressed.

[Example 5]
In the fifth embodiment, when the borderless printing mode which is the special mode is selected, the secondary transfer roller 22 is not separated from the intermediate transfer belt 10 in the inter-paper area on the intermediate transfer belt 10. In addition, the secondary transfer bias is alternately switched between the bias having the same polarity and the bias having the opposite polarity as in normal printing in the inter-paper region. Thus, the toner attached to the secondary transfer roller 22 is retransferred to the intermediate transfer belt 10 in the inter-paper area. In this embodiment, the toner pattern is not formed in the inter-paper area during continuous printing.

  FIG. 15 is an explanatory diagram illustrating the control contents of the secondary transfer contact / separation control and the secondary transfer bias switching control in the inter-sheet region in the present embodiment. This figure shows the switching timing of the secondary transfer bias by the secondary transfer bias application power source 90 in the inter-sheet area on the intermediate transfer belt 10 in this embodiment, with the horizontal axis as time. During normal printing, a negative bias having the same polarity as the negative charging polarity of the toner is applied to the driven roller 16 by the secondary transfer bias applying power supply 90.

  In this embodiment, the secondary transfer bias is switched first after the trailing edge of the preceding sheet P1 has passed through the contact portion between the secondary transfer roller 22 and the intermediate transfer belt 10, and then the secondary transfer bias is switched from minus to plus ( Time A) in FIG. The time T1 for applying the positive bias is such that the distance D1 when “distance D1 = rotational speed of the secondary transfer roller 22 × time T1” is longer than at least the circumference of the secondary transfer roller 22. (Between time B and time C in FIG. 15).

  Next, the secondary transfer bias is switched from plus to minus (time C in FIG. 15). The time T2 for applying the negative bias is such that the distance D2 when “distance D2 = rotational speed of the secondary transfer roller 22 × time T2” is at least longer than the circumference of the secondary transfer roller 22. (Between time D and time E in FIG. 15).

  Thereafter, the secondary transfer bias is switched again from minus to plus (time E in FIG. 15). The time T1 for applying the positive bias is such that the distance D1 when “distance D1 = rotational speed of the secondary transfer roller 22 × time T1” is longer than at least the circumference of the secondary transfer roller 22. (Between time F and time G in FIG. 15).

  Thereafter, the secondary transfer bias is again switched from plus to minus (time G in FIG. 15). Further, the time T2 for applying the negative bias is such that the distance D2 when “distance D2 = rotational speed of the secondary transfer roller 22 × time T2” is at least longer than the circumference of the secondary transfer roller 22. (Between time H and time I in FIG. 15).

  Before the leading edge of the next trailing sheet P2 is input to the secondary transfer area, the switching of the secondary transfer bias from the plus bias to the minus bias is completed, and the toner removal operation of the secondary transfer roller 22 is completed. (Time I in FIG. 15). If the secondary transfer bias at time D in FIG. 15 is different from the normal output, the secondary transfer bias is set to the normal output before the next sheet leading edge is input to the secondary transfer area. To do.

  By the bias switching operation at time A and time E in FIG. 15, the negatively charged toner attached to the surface of the secondary transfer roller 22 is retransferred to the intermediate transfer belt 10, and the toner on the surface of the secondary transfer roller is removed. The By making the distance D1 longer than the circumference of the secondary transfer roller 22, negatively charged toner on the entire circumference of the secondary transfer roller 22 can be removed.

  Further, by the bias switching operation at time C and time G in FIG. 15, the positively charged toner attached to the surface of the secondary transfer roller 22 is retransferred to the intermediate transfer belt 10, and the toner on the surface of the secondary transfer roller is transferred. Removed. Normally, the charging polarity of the toner is negative, but the charging polarity may change and become positive charging due to a discharge phenomenon that occurs in the transfer process, so this positively charged toner is removed. By making the distance D <b> 2 longer than the circumference of the secondary transfer roller 22, the positively charged toner on the entire circumference of the secondary transfer roller 22 can be removed.

  In the borderless printing mode, the toner is reattached from the surface of the secondary transfer roller 22 to the intermediate transfer belt 10 in the inter-paper area, and the toner attached to the surface of the secondary transfer roller 22 is removed, thereby making the paper back stain. Can be suppressed.

  In the present embodiment, the distance between the paper regions is set to be at least four times the circumference of the secondary transfer roller 22, but at least twice the circumference of the secondary transfer roller 22. Is preferred. This is because it is necessary to perform retransfer for one turn of the secondary transfer roller with a plus bias and a minus bias. Actually, a distance that takes into account the time required for switching the bias is necessary.

[Example 6]
In the sixth embodiment, when printing without a trailing edge is performed, the distance between the sheets is longer than that of the normal printing by one rotation of the secondary transfer roller, for example, compared with the normal printing. The distance between the sheets is increased by 1.2 rotations of the secondary transfer roller.

  In printing without a trailing edge, an image is formed so as to protrude from the trailing edge of the paper P, so that the toner protruding from the trailing edge of the paper P adheres to the intermediate transfer belt 10. Therefore, when an image is transferred from the intermediate transfer belt 10 to the paper P in the secondary transfer region, the protruding toner adheres to the surface of the secondary transfer roller 22 from the intermediate transfer belt 10. Therefore, the toner adhering to the surface of the secondary transfer roller 22 adheres to the back surface of the paper P that is subsequently conveyed to the secondary transfer region, and the paper back is contaminated by the protruding toner.

  Therefore, in this embodiment, when performing printing without a trailing edge, the secondary transfer bias is switched between the bias having the same polarity and the reverse polarity as in normal printing in the inter-paper region, and the secondary transfer roller 22. The toner adhered to the intermediate transfer belt 10 is reattached to the intermediate transfer belt 10 in the inter-paper region.

  FIG. 16 shows a flowchart of the secondary transfer contact / separation control and the secondary transfer bias switching control in the inter-sheet region when the trailing edgeless printing is performed and when the trailing edgeless printing is not performed. In the present embodiment, it is assumed that an image forming mode for executing printing with margins and an image forming mode for executing printing without trailing edge can be executed.

  FIG. 17 is an explanatory diagram showing the control contents of the secondary transfer contact / separation operation and the secondary transfer bias switching control when the trailing edgeless printing is set in this embodiment. In FIG. 17, the horizontal axis represents time, the timing at which the paper P, toner image, and toner pattern TP pass through the secondary transfer region, the contact / separation timing of the secondary transfer roller 22, and the secondary transfer bias application power supply 90. The next transfer bias switching timing is shown.

  Further, the control contents of the secondary transfer contact / separation operation and the secondary transfer bias switching control when the trailing edgeless printing in this embodiment is not set are the same as those shown in FIG. is there.

  In the control flow shown in FIG. 16 in this embodiment, first, after the trailing edge of the preceding sheet P1 passes through the secondary transfer area (S1), the trailing edge of the sheet regardless of whether or not the trailing edge printing is selected. After passing through the secondary transfer region, the secondary transfer roller 22 is separated from the intermediate transfer belt 10 with a certain interval. Further, during this separation, the secondary transfer bias applied by the secondary transfer bias application power source 90 is switched to a bias having a polarity opposite to that during normal printing (a bias having a positive polarity) (S2) (time in FIG. 12). A, time A) in FIG. When the toner pattern TP is input to the secondary transfer region, the secondary transfer bias is set to be positive (time B in FIG. 12, time B in FIG. 17).

  The reason why the secondary transfer roller 22 is spaced apart from the intermediate transfer belt 10 at a certain interval is that the following problems may occur. In other words, if the separation operation in the secondary transfer area is performed immediately after the trailing edge of the sheet passes through the secondary transfer area, the separation operation is performed while the sheet is still in the secondary transfer area depending on variations in the sheet conveyance timing. This is because there is a possibility of causing image defects.

  Next, it is determined whether the rear end of the toner pattern TP has passed through the secondary transfer region and a certain time has passed (S3). If it is determined that a certain time has elapsed (YES in S3), it is determined whether printing without trailing edge is selected (S4).

  The selection of the printing without the trailing edge includes, for example, an image forming mode in which the operator performs printing with a border and an image forming mode in which printing without the trailing edge is executed on the operation unit provided in the copier body 1. Select by pressing the button to switch.

  If it is determined that the trailing edgeless printing is selected (YES in S4), the contact operation of the secondary transfer roller 22 to the intermediate transfer belt 10 is started (S5) (time C in FIG. 17). Then, after waiting for a running time of 1.2 rotations of the secondary transfer roller after the start of the contact operation (S6), the secondary transfer bias applied by the secondary transfer bias application power source 90 is applied during normal printing. Switching to bias (negative polarity bias) (S7) (time D in FIG. 17). Then, before the leading edge of the next succeeding paper P2 is input to the secondary transfer area, the secondary transfer bias is set to the normal output (time E in FIG. 17).

  On the other hand, if it is determined that printing without trailing edge is not selected (NO in S4), the contact operation of the secondary transfer roller 22 to the intermediate transfer belt 10 is started (S8). At the same time, the secondary transfer bias applied by the secondary transfer bias application power supply 90 is switched to a normal printing bias (negative polarity bias) (time C in FIG. 12). Then, the secondary transfer bias is set to the normal output before the leading edge of the next succeeding paper P2 is input to the secondary transfer area (time D in FIG. 12).

  When printing without a trailing edge, the distance between the sheets is increased by increasing the distance between the sheets as compared with the normal printing, and the switching of the secondary transfer bias after the toner patch TP passes through the secondary transfer area is usually performed. Is delayed by 1.2 rotations of the secondary transfer roller from the time of printing. As a result, as shown in FIG. 17, the state where the secondary transfer roller 22 is in contact with the intermediate transfer belt 10 and the secondary transfer bias is positive continues for one rotation of the secondary transfer roller or more. As a result, cleaning by retransfer of the toner adhering to the surface of the secondary transfer roller to the intermediate transfer belt 10 can be performed over the entire circumference of the secondary transfer roller.

  Note that when performing printing without trailing edge, how much the inter-paper area can be widened compared to normal printing without trailing edge printing is the secondary transfer roller. It depends on the switching time of the roller 22. However, it is necessary to widen at least one rotation of the secondary transfer roller as compared with normal printing.

[Example 7]
In the seventh embodiment, when printing without a trailing edge is performed, the distance between the sheets is longer than that of the normal printing by two rotations of the secondary transfer roller, for example, compared to the normal printing. The distance between the sheets is increased by three rotations of the secondary transfer roller. In addition, when performing printing without a trailing edge, the secondary transfer bias is alternately switched between the bias having the same polarity and the bias having the reverse polarity in the inter-paper area and adhered to the secondary transfer roller 22. The toner is reattached to the intermediate transfer belt 10 in the inter-paper area.

  FIG. 18 shows a flowchart of the secondary transfer contact / separation control and the secondary transfer bias switching control in the inter-paper region when the trailing edgeless printing is performed and when the trailing edgeless printing is not performed. In the present embodiment, it is assumed that an image forming mode for executing printing with margins and an image forming mode for executing printing without trailing edge can be executed.

  FIG. 19 is an explanatory diagram showing the control contents of the secondary transfer contact / separation operation and the secondary transfer bias switching control when the trailing edgeless printing is set in this embodiment. In FIG. 19, the horizontal axis represents time, the timing at which the paper P, toner image, and toner pattern TP pass through the secondary transfer region, the contact / separation timing of the secondary transfer roller 22, and the secondary transfer bias application power supply 90. The next transfer bias switching timing is shown.

  The control contents of the secondary transfer contact / separation operation and the secondary transfer bias switching control when the trailing edgeless printing is not set in this embodiment are the same as those shown in FIG. is there.

  In the control in the present embodiment, first, after the trailing edge of the preceding sheet P1 passes through the secondary transfer area (S1), the trailing edge of the sheet passes through the secondary transfer area regardless of whether or not the trailing edge printing is selected. After passing, the secondary transfer roller 22 is separated from the intermediate transfer belt 10 with a certain interval. Further, during this separation, the secondary transfer bias applied by the secondary transfer bias application power source 90 is switched to a bias having a polarity opposite to that during normal printing (a bias having a positive polarity) (S2) (time in FIG. 12). A, time A) in FIG. When the toner pattern TP is input to the secondary transfer region, the secondary transfer bias is set to be positive (time B in FIG. 12, time B in FIG. 19).

  Next, it is determined whether the rear end of the toner pattern TP has passed through the secondary transfer region and a certain time has passed (S3). If it is determined that a certain time has elapsed (YES in S3), it is determined whether printing without trailing edge is selected (S4).

  If it is determined that printing without the trailing edge is selected (YES in S4), the contact operation of the secondary transfer roller 22 to the intermediate transfer belt 10 is started (S5). In addition, the secondary transfer bias applied by the secondary transfer bias application power supply 90 together with this contact operation is switched to a normal printing bias (negative polarity bias) (S6) (time C in FIG. 19).

  Then, after waiting for time T1 from the time of switching the bias, the secondary transfer bias applied by the secondary transfer bias application power supply 90 is switched to a bias having a polarity opposite to that during normal printing (a positive polarity bias) (S7). (Time D in FIG. 19). Then, after waiting for time T2 from the time of this bias switching, the secondary transfer bias applied by the secondary transfer bias application power supply 90 is switched to the bias at the time of normal printing (negative polarity bias) (S8) (FIG. 19). Time E). Then, after waiting for time T1 from the time of switching the bias, the secondary transfer bias applied by the secondary transfer bias applying power supply 90 is switched to a bias having a polarity opposite to that during normal printing (a positive polarity bias) (S9). (Time F in FIG. 19).

  Then, after waiting for time T2 from the time of switching the bias (S10), the secondary transfer bias applied by the secondary transfer bias application power supply 90 is switched to a bias during normal printing (a negative polarity bias) (S10). (Time G in FIG. 19).

  Then, before the leading edge of the next succeeding paper P2 is input to the secondary transfer area, the secondary transfer bias is set to the normal output (time H in FIG. 19).

  On the other hand, if it is determined that printing without trailing edge is not selected (NO in S4), the contact operation of the secondary transfer roller 22 to the intermediate transfer belt 10 is started (S12). At the same time, the secondary transfer bias applied by the secondary transfer bias application power supply 90 is switched to a normal printing bias (negative polarity bias) (S11) (time C in FIG. 12). Then, the secondary transfer bias is set to the normal output before the leading edge of the next succeeding paper P2 is input to the secondary transfer area (time D in FIG. 12).

  As shown in FIG. 19, the state where the secondary transfer roller 22 is in contact with the intermediate transfer belt 10 and the secondary transfer bias is negative exists as a whole for 2 × T1 ′ time. Further, the state where the secondary transfer roller 22 is in contact with the intermediate transfer belt 10 and the secondary transfer bias is positive exists as a whole for 2 × T2 ′ time.

  When printing without a trailing edge, the distance between the sheets is increased by increasing the distance between the sheets as compared with the normal printing, and the switching of the secondary transfer bias after the toner patch TP passes through the secondary transfer area is usually performed. Is delayed by three rotations of the secondary transfer roller from the time of printing. As a result, the following equations 1 and 2 were satisfied.

  By satisfying the above formula 1, cleaning by retransfer of negatively charged toner adhering to the surface of the secondary transfer roller to the intermediate transfer belt 10 can be performed over the entire circumference of the secondary transfer roller. Further, by satisfying the above formula 2, it is possible to perform cleaning by retransfer to the intermediate transfer belt 10 over the entire circumference of the secondary transfer roller even for the positively charged toner.

  Note that when performing printing without trailing edge, how much the inter-paper area can be widened compared to normal printing without trailing edge printing is the secondary transfer roller. It depends on the switching time of the roller 22. However, it is necessary to widen at least two rotations of the secondary transfer roller as compared with normal printing.

  In this embodiment, the total number of times of switching between the minus and plus of the secondary transfer bias in the inter-sheet area is 6 when performing printing without a trailing edge. However, the present invention is not limited to this. That is, in the state where the secondary transfer roller 22 and the intermediate transfer belt 10 are in contact with each other, a negative secondary transfer bias is applied more than one rotation of the secondary transfer roller, and a positive secondary transfer bias is applied to the secondary transfer roller 1. What is necessary is just to make it rotate or more. If this is satisfied, the number of times of switching between minus and plus of the secondary transfer bias is not limited.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
An image bearing member such as an intermediate transfer belt 10 that is rotatably provided and carries a toner image on the surface thereof, and a transfer member such as a secondary transfer roller 22 that is disposed to face the image bearing member, continuously form an image. In an image forming apparatus such as a printer having a non-transfer toner adhering means for adhering a non-transfer toner that is not transferred onto a sheet to an inter-paper area existing on the image carrier during a continuous image forming period, the transfer member is It is a foaming roller, and has contact / separation means such as a secondary transfer contact / separation mechanism 70 for contacting and separating the foaming roller and the image carrier so that there is no margin at the edge or any edge of the entire circumference of the paper. A special mode for performing borderless printing for forming a toner image up to the edge of the paper, and a normal mode for performing bordered printing for forming a toner image so that there is a margin on the entire periphery of the paper, when the special mode, Zo担When the sheet spacing region existing on the image carrier as the body rotates passes through the transfer region where the image carrier and the transfer member face each other, the contact / separation means causes the image carrier and the image carrier to The contact / separation operation for separating the transfer member is not performed, and the contact / separation operation is performed in the normal mode.
According to this , as described in the above embodiment, the non-transfer toner adhered to the inter-paper area on the image carrier while suppressing the occurrence of an abnormal image due to the vibration caused by the collision between the transfer member and the paper. It is possible to suppress the occurrence of stains on the back side of the paper due to.
(Aspect B)
In (Aspect A), when the image is formed on a specific sheet, the contact / separation unit continuously forms the image on the transfer member and the image carrier before the leading edge of the specific sheet enters the transfer area. The transfer member and the image carrier are brought into contact with each other after the leading edge of a specific sheet enters the transfer region. According to this, as described in the above embodiment, since the transfer member and the image carrier are separated from each other when the specific sheet enters the transfer area, the front end of the specific sheet is at the entrance of the transfer area. There will be no situation of collision. Therefore, it is possible to prevent the image quality from being deteriorated due to the vibration caused by the collision being transmitted to the image carrier.
(Aspect C)
In (Aspect A) or (Aspect B), a secondary transfer bias applying power supply 90 for applying a transfer bias to form a transfer electric field for transferring the toner image on the image carrier to the paper side in the transfer region, etc. A transfer bias applying means, and when the inter-paper area during continuous image formation passes through the transfer area, the contact member separates the transfer member from the image carrier. In this case, the transfer bias unit applies a bias having a reverse polarity to that during normal image formation. According to this, as described in the above embodiment, it is difficult for the toner to fly from the image bearing member toward the transfer member, and toner contamination on the transfer member can be suppressed.
(Aspect D)
In (Aspect C), the transfer bias applied by the transfer bias applying unit is controlled at a constant voltage while the transfer member and the image carrier are separated from each other. According to this, as described in the above embodiment, it is possible to suppress the flying of the toner to the transfer member and to suppress the problems associated with the abnormal increase in voltage.
(Aspect E)
In any one of (Aspect A) to (Aspect D), the non-transfer toner adhering unit forms a toner pattern for density adjustment control as the non-transfer toner, and a plurality of toners constituting the toner pattern A toner adhesion amount detection unit such as a toner adhesion amount sensor 5 for detecting the toner adhesion amount adhering to each patch, and a density adjustment control unit for performing image density adjustment control based on the detection result of the toner adhesion amount detection unit Density adjustment control means such as 80. According to this, as described in the above embodiment, the image density during continuous image formation can be stabilized. In addition, the back side of the paper is not stained by the toner pattern.
(Aspect F)
In any one of (Aspect A) to (Aspect E), the non-transfer toner adhering unit forms a toner consumption pattern for replacing the toner accommodated in the non-transfer toner adhering unit as the non-transfer toner. According to this, as described in the above embodiment, the deteriorated toner can be refreshed with new toner, and the image quality can be stabilized. In addition, the backside of the paper due to the toner consumption pattern does not occur.
(Aspect G)
In any one of (aspect A) to (embodiment F), can be selected operator and the normal mode and the special mode is optional, and when the special mode is selected, at the time of continuous image formation In the inter-paper region, the transfer member and the image carrier are brought into contact with each other by the contact / separation unit, and the non-transfer toner is applied to the inter-paper region of the image carrier by the non-transfer toner attaching unit. Do not adhere. According to this, as described in the above embodiment, the toner on the surface of the transfer member can be removed by transferring the toner from the transfer member to the image carrier in the inter-paper region. Further, when this special mode is selected, the toner on the transfer member due to the non-transfer toner can be prevented by not attaching the non-transfer toner to the inter-paper area.
(Aspect H)
In (Aspect G), when the special mode is selected, the transfer bias has a polarity opposite to that when the image is transferred from the image carrier to the paper in the inter-paper area during continuous image formation. Apply a bias. According to this, as described in the above embodiment, the toner is reattached to the image carrier from the surface of the transfer member in the inter-paper region, and the toner attached to the surface of the transfer member is removed, so that Contamination can be suppressed.
(Aspect I)
In (Aspect G), when the special mode is selected, the transfer bias is set to have the same polarity as that when the image is transferred from the image carrier to the paper in the inter-paper area during continuous image formation. A bias and a reverse polarity bias are alternately switched and applied. According to this, as described in the above embodiment, the toner charged to the image carrier with the same polarity and the opposite polarity is reattached from the surface of the transfer member to the surface of the transfer member in the inter-paper region. By removing the toner that has been removed, it is possible to suppress the occurrence of stains on the back of the paper .
( Aspect J)
In any one of (Aspect G) to (Aspect I) , in the special mode, the width in the rotation direction of the image carrier in the inter-paper region is wider than that in the normal mode. According to this, as described in the above embodiment, the toner attached to the surface of the transfer member can be removed more reliably.
(Aspect K)
In (Aspect J) , in the special mode, the width in the image carrier rotating direction of the inter-paper region is set to be twice or more the circumference of the foam roller. According to this, as described in the above embodiment, when the toner charged to the same polarity and the opposite polarity is present on the surface of the transfer member, the bias having the same polarity and the bias having the opposite polarity are provided. It is desirable to alternately apply at least one rotation of each roller. Therefore, by setting the width of the inter-paper region to be twice or more the circumference of the foaming roller, it is possible to more reliably remove the toner having the same polarity and the opposite polarity.
(Aspect L)
In any one of (Aspect A) to (Aspect F), a toner image is formed up to the rear end of the paper so that no margin is left at the rear edge of the paper in the paper transport direction. According to this, as described in the above embodiment, it is possible to suppress the occurrence of stains on the back of the sheet due to the stain on the transfer member due to the toner protruding from the rear end of the sheet.
(Aspect M)
In (Mode L) , the first image forming mode in which a toner image is formed on the paper so that there is a margin on the entire periphery of the paper, and the trailing edge of the paper so that there is no margin on the trailing edge of the paper. A second image forming mode for forming a toner image, and when the image is formed in the second image forming mode, the image in the inter-sheet area is more than in the case where the image is formed in the first image forming mode. The width in the rotation direction of the carrier is increased. According to this, as described in the above embodiment, the toner attached to the surface of the transfer member can be removed more reliably.
(Aspect N)
In (Aspect M) , when image formation is performed in the second image formation mode, the width of the inter-paper region in the rotation direction of the image carrier is larger than that in the case where image formation is performed in the first image formation mode. Make it wider than the circumference. According to this, as described in the above embodiment, the toner attached to the transfer member is reattached from the surface of the transfer member to the image carrier in the inter-paper region, and the toner is applied over the entire circumference of the transfer member. It is possible to secure a time for removing. Therefore, it is possible to more reliably suppress the occurrence of paper back contamination.
(Aspect O)
In (Aspect N) , when image formation is performed in the second image formation mode, the image carrier and the foaming roller are in contact with each other in the inter-paper region, and the reverse of the first image formation mode. The time for applying the polar bias is set to be at least the time required for one rotation of the foaming roller. According to this, as described in the above embodiment, the toner having the reverse polarity can be more reliably removed from the entire circumference of the transfer member.
(Aspect P)
In (Aspect M) , when image formation is performed in the second image formation mode, the width of the inter-paper region in the rotation direction of the image carrier is larger than that in the case where image formation is performed in the first image formation mode. Make it wider than twice the circumference of According to this, as described in the above embodiment, it is possible to secure the time for removing the toner adhering to the transfer member over the entire circumference of the transfer member, and to more reliably prevent the back side of the paper from being stained. Can be suppressed.
(Aspect Q)
In (Aspect N) or (Aspect P) , when image formation is performed in the second image formation mode, the image carrier and the foaming roller are in contact with each other in the inter-paper area, and the first image A time for applying a bias having a polarity opposite to that of the forming mode is set to be at least a time required for one rotation of the foaming roller, the image carrier and the foaming roller are in contact with each other, and the first image The time for applying the bias having the same polarity as that of the forming mode is set to be at least the time required for one rotation of the foaming roller. According to this, as described in the above embodiment, the toner having the same polarity and the opposite polarity can be more reliably removed from the entire circumference of the transfer member.
(Aspect R)
In any one of (Aspect A) to (Aspect Q) , the foaming roller is configured using a foaming member such as NBR rubber having an Asker C hardness of 60 [°] or less. According to this, as described in the above embodiment, the generation of jitter can be suppressed.
(Aspect S)
In (Aspect R) , the Asker C hardness of the foamed member is 45 [°] or less. According to this, as described in the above embodiment, the jitter can be improved to a state where it cannot be visually observed.
(Aspect T)
In any one of (Aspect A) to (Aspect S) , the transfer member is rotationally driven by a drive mechanism different from the image carrier. According to this, as described in the above embodiment, when the thick paper as the paper enters the transfer nip, the drive from the drive source provided in the drive mechanism of the transfer member assists the rotational drive of the image carrier. As a result, the speed fluctuation of the image carrier can be reduced. Accordingly, it is possible to reduce the shock jitter accompanying the speed fluctuation of the image carrier.
(Aspect U)
In any one of (Aspect A) to (Aspect T) , the contact / separation means has different separation distances between the image carrier and the transfer member when the image carrier and the transfer member are separated from each other. The above separation operation is performed, and the image carrier and the transfer member are separated even during normal separation other than separation in the inter-paper region during continuous image formation, and the paper during continuous image formation is separated. When the image carrier and the transfer member are separated from each other in the intermediate region, the separation distance between the image carrier and the transfer member is shorter than when the image carrier and the transfer member are separated from each other during the normal separation. According to this, as described in the above embodiment, the forcibly discharged toner immediately after completion of continuous image formation adheres to the transfer member while achieving both the adhesion of the untransferred toner to the transfer member and the improvement of the contact / separation operation speed. Can be suppressed.
(Aspect V)
In (Aspect U) , the contact / separation means is in any of the separated states during the contact operation of shifting the image carrier and the transfer member from the separated states to the contact state by the two or more separated operations. It is configured to shift to the contact state by one operation and to shift to any separation state by one operation at the time of the separation operation to shift from the contact state to each separation state. According to this, as described in the above embodiment, the effect of (Aspect U) can be realized with a simple configuration of the contact / separation means.
(Aspect W)
In (Aspect V) , the contact / separation means includes a cam member such as a contact / separation cam 72 disposed so that a cam surface contacts a cam contact position provided on the transfer member, and a predetermined rotation of the cam member. It is comprised with rotation drive means, such as a contact / separation motor rotated to a position. According to this, as described in the above embodiment, the effect of (Aspect V) is realized with a simple configuration of the contacting / separating means.

DESCRIPTION OF SYMBOLS 1 Copier body 2 Paper feed table 3 Scanner 4 Automatic document feeder 5 Toner adhesion amount sensor 10 Intermediate transfer belt 14 Drive roller 15 Drive roller 16 Drive roller 17 Intermediate transfer belt cleaning device 18 Image forming unit 19 Oscillating member 20 Transfer Device 21 Exposure device 22 Secondary transfer roller 22a Secondary transfer roller shaft 23a Tension roller 23b Tension roller 24 Conveyor belt 25 Fixing device 26 Fixing belt 27 Pressure roller 28 Paper reversing device 29 Swing shaft 30 Document table 32 Contact glass 33 First traveling body 34 Second traveling body 35 Imaging lens 36 Reading sensor 40 Photosensitive body 42 Paper feed roller 43 Paper bank 44 Paper feed cassette 45 Separating roller 46 Paper feed path 47 Transport roller 48 Paper feed path 49 Registration roller pair 50 Manual feed roller 51 hand Paper tray 52 manual separation roller 53 paper feed path 55 switching claw 56 discharge roller 57 paper discharge tray 60 charging device 61 developing device 62 primary transfer device 63 photoconductor cleaning device 64 static eliminating device 70 secondary transfer contact / separation mechanism 71 contact / separation cam 71a Rotation shaft 72 Contact / separation cam 72a Rotation shaft 73 Contact / separation cam 73a Rotation shaft 74 Oscillation arm 75 Oscillation fulcrum 76 Spring 77 Contact / separation cam 77a Rotation shaft 78 Contact plate 80 Density adjustment control unit 81 Development bias application device 82 Charging bias Application device 90 Secondary transfer bias application power supply 95 Toner supply device 96 Toner supply motor

JP 2001-305823 A JP 2001-31154 A

Claims (23)

An image carrier that is rotatably provided and carries a toner image on a surface thereof, a transfer member that is disposed to face the image carrier, and a continuous image forming period in which images are continuously formed on the image carrier. In addition, an image forming apparatus provided with non-transfer toner attaching means for attaching non-transfer toner that is not transferred to paper to an inter-paper region existing on the image carrier,
The transfer member is a foam roller;
Having contact / separation means for contacting and separating the foam roller and the image carrier;
A special mode for borderless printing that forms a toner image up to the edge of the paper so that there is no margin at the edge or any edge of the paper, and a toner image that has a margin at the edge of the paper A normal mode for performing printing with a border,
In the special mode, the sheet-to-paper area existing on the image carrier as the image carrier is rotated passes through the transfer area where the image carrier and the transfer member face each other. Without performing a contact / separation operation of separating the image carrier and the transfer member by a separating means;
An image forming apparatus that performs the contact / separation operation in the normal mode. The image forming apparatus according to claim 1.
When the image is formed on a specific sheet, the contact / separation unit connects the transfer member and the image carrier between the sheets at the time of continuous image formation before the leading edge of the specific sheet enters the transfer area. An image forming apparatus, wherein the transfer member and the image carrier are brought into contact with each other after the leading edge of the specific sheet enters the transfer region. The image forming apparatus according to claim 1 or 2,
A transfer bias applying means for applying a transfer bias to form a transfer electric field for transferring the toner image on the image carrier to the paper side in the transfer region;
While the inter-paper area during continuous image formation passes through the transfer area, the polarity is opposite to that during normal image formation while the transfer member and the image carrier are separated by the contact / separation means. The image forming apparatus is characterized in that the transfer bias applying means applies the above bias. The image forming apparatus according to claim 3.
The image forming apparatus, wherein the transfer bias applied by the transfer bias applying means is controlled at a constant voltage while the transfer member and the image carrier are separated from each other. The image forming apparatus according to any one of claims 1 to 4,
The non-transfer toner adhering means forms a toner pattern for density adjustment control as the non-transfer toner,
Toner adhesion amount detection means for detecting the amount of toner adhesion to each of a plurality of toner patches constituting the toner pattern;
An image forming apparatus comprising: a density adjustment control unit that executes image density adjustment control based on a detection result of the toner adhesion amount detection unit. The image forming apparatus according to any one of claims 1 to 4,
The non-transfer toner attaching unit forms a toner consumption pattern for replacing the toner stored in the non-transfer toner attaching unit as the non-transfer toner. The image forming apparatus according to any one of claims 1 to 6,
An operator can arbitrarily select the normal mode and the special mode,
When the special mode is selected, the transfer member and the image carrier are brought into contact with each other by the contact / separation means in the inter-paper area during continuous image formation, and the non-transfer toner adheres. An image forming apparatus, wherein the non-transfer toner is not adhered to the inter-paper area of the image carrier by means. The image forming apparatus according to claim 7.
Transfer bias applying means for applying a transfer bias to form a transfer electric field for transferring the toner image on the image carrier to the paper side in a transfer region where the image carrier and the transfer member face each other. cage, said if a particular mode is selected, in the inter-sheet region during continuous image formation, to apply a reverse polarity of the bias than when transferring an image on a sheet of the transfer bias from the image carrier An image forming apparatus. The image forming apparatus according to claim 7.
Transfer bias applying means for applying a transfer bias to form a transfer electric field for transferring the toner image on the image carrier to the paper side in a transfer region where the image carrier and the transfer member face each other. cage, said if a particular mode is selected, in the inter-sheet region during continuous image formation, the transfer bias, of the same polarity as when transferring an image on a sheet from the image carrier bias and reverse polarity The image forming apparatus is characterized in that the bias is alternately switched and applied. The image forming apparatus according to any one of claims 7 to 9,
In the special mode, the width in the rotation direction of the image carrier in the inter-paper region is wider than that in the normal mode. The image forming apparatus according to claim 10.
In the special mode, the width in the rotation direction of the image carrier in the inter-paper region is at least twice the circumference of the foam roller. The image forming apparatus according to any one of claims 1 to 6,
An image forming apparatus, wherein a toner image is formed up to a rear end of a sheet such that a margin is eliminated at a rear end edge of the sheet in a sheet transport direction. The image forming apparatus according to claim 12.
A first image forming mode in which a toner image is formed on the paper so that there is a margin on the entire periphery of the paper, and a toner image is formed up to the rear edge of the paper so that there is no margin on the trailing edge of the paper. And a second image forming mode.
When image formation is performed in the second image formation mode, the width in the image carrier rotation direction of the inter-paper region is wider than when image formation is performed in the first image formation mode. apparatus. The image forming apparatus according to claim 13.
When image formation is performed in the second image formation mode, the width in the image carrier rotation direction of the inter-paper region is wider than the circumference of the foaming roller than when image formation is performed in the first image formation mode. An image forming apparatus. The image forming apparatus according to claim 14.
When image formation is performed in the second image formation mode, the image carrier and the foaming roller are in contact with each other in the inter-paper region, and a bias having a polarity opposite to that of the first image formation mode is applied. An image forming apparatus characterized in that at least the time required for one rotation of the foaming roller is provided. The image forming apparatus according to claim 13.
When image formation is performed in the second image formation mode, the width in the rotation direction of the image carrier in the inter-paper region is twice the circumference of the foaming roller than when image formation is performed in the first image formation mode. An image forming apparatus characterized by being widened as described above. The image forming apparatus according to claim 14 or 16,
When image formation is performed in the second image formation mode, the image carrier and the foaming roller are in contact with each other in the inter-paper region, and a bias having a polarity opposite to that of the first image formation mode is applied. The time is set longer than at least the time required for one rotation of the foaming roller, and the image carrier and the foaming roller are in contact with each other and the bias having the same polarity as that of the first image forming mode is applied. Is provided for at least the time required for one rotation of the foaming roller. The image forming apparatus according to claim 1,
An image forming apparatus comprising the foaming roller using a foaming member having an Asker C hardness of 60 [°] or less. The image forming apparatus according to claim 18.
An image forming apparatus, wherein the foam member has an Asker C hardness of 45 [°] or less. The image forming apparatus according to any one of claims 1 to 19,
The image forming apparatus, wherein the transfer member is rotationally driven by a driving mechanism different from the image carrier. The image forming apparatus according to any one of claims 1 to 20,
The contact / separation means performs two or more separation operations in which the separation distance between the image carrier and the transfer member is different when the image carrier and the transfer member are separated from each other. The image carrier and the transfer member are separated from each other even during normal separation other than separation in the inter-paper region at the time of formation,
When the image carrier and the transfer member are separated from each other in the inter-paper area during the continuous image formation, the image carrier is more separated than when the image carrier and the transfer member are separated during the normal separation. An image forming apparatus characterized in that a separation distance between the transfer member and the transfer member is short. The image forming apparatus according to claim 21, wherein
The contact / separation means contacts the image carrier and the transfer member in a single operation from any of the separated states during the contact operation of shifting from the separated state to the contact state by the two or more separated operations. An image forming apparatus configured to shift to any of the separated states during a separation operation that shifts to a state and shifts from the contact state to each separated state. The image forming apparatus according to claim 22, wherein
The contact / separation means includes a cam member arranged so that the cam surface comes into contact with a cam contact position provided on the transfer member, and a rotation drive means for rotating the cam member to a predetermined rotation position. An image forming apparatus.

Images