JP6283982B2 - Image forming system - Google Patents

Description

  The present invention relates to an image forming system including an image forming apparatus such as a printer, a copying machine, and a facsimile machine. More specifically, the present invention relates to an image forming system that transfers an image toner image and a sticking toner image based on image information to a sheet, The present invention relates to an image forming system including a sheet binding device that forms an image on a sheet and binds a binding portion between sheets by a sticking force of a sticking toner image to bind a plurality of sheets.

  A conventional image forming system is known as a type of post-processing apparatus for an electrophotographic image forming apparatus that uses a sheet binding device that binds a plurality of sheets using toner as an adhesive (patent). Document 1, Patent Document 2, etc.). In this type of sheet binding apparatus, a sticking toner image is formed on an end portion (binding portion) of a sheet on which an image is formed, and the binding portion of the stacked sheet bundle is heated to form a sticking toner image. The sheets are stuck together by melting. In such a toner binding device, it is an important issue to obtain as much sticking force as possible with the melted toner.

  Patent Document 2 discloses a sheet binding device that forms a sticking toner image on both sides of a binding portion of each sheet by using a duplex copying mode in which an original image is formed on both sides of a sheet. According to this sheet binding device, the amount of toner per unit area interposed between the two sheets as compared to the case where a sticking toner image is formed only on one binding margin of two sheets to be stuck. Can be increased. Therefore, a larger amount of toner can be interposed within a limited area of the binding margin, and a large sticking force by the sticking toner image can be obtained.

  Further, in Patent Document 2, a multiple copy mode in which a plurality of toner images are superimposed on one side of a sheet to form a document image is used for pasting to one binding portion of two sheets to be pasted. A sheet binding device that forms toner images in an overlapping manner is disclosed. According to this sheet binding device, the toner per unit area interposed between the two sheets is compared with the case where one sticking toner image is formed on one binding margin of two sheets to be stuck. The amount can be increased. Also in this sheet binding apparatus, more toner can be interposed within a limited area of the binding margin, and a large sticking force by the sticking toner image can be obtained.

  However, in any of the sheet binding apparatuses disclosed in Patent Document 2, the pasting toner image formed on the binding margin portion of the sheet is a normal image forming operation for forming a document image (double-sided copying mode, multiple copying mode). ). Therefore, the maximum toner adhesion amount (maximum toner amount deposited per unit area) of the sticking toner image cannot exceed the maximum toner adhesion amount of the document image formed by the image forming operation. For this reason, there is a problem that it is impossible to form a sticking toner image with a large amount of toner adhesion amount (toner adhesion amount per unit area) that exceeds the maximum toner amount of the document image and obtain a larger adhesion force. .

  In particular, when a sheet such as poor recycled paper is bound in a low humidity environment, the maximum toner of an image formed by the image forming operation when the sheet condition or environmental condition is unfavorable for obtaining a large sticking force. Even with a sticking toner image formed with an adhesion amount, only sticking power comparable to sticky paper may be obtained, and it is difficult to obtain sufficient sticking power. In addition, this problem is serious because recent image forming apparatuses tend to reduce the maximum toner amount of a formed image.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to replace a toner image for affixing with a toner adhesion amount exceeding the maximum toner adhesion amount per unit area of the image toner image. It is an object of the present invention to provide an image forming system that can be attached to a portion and obtain a larger sticking force.

In order to achieve the above object, according to the present invention, an image toner image based on image information and a sticking toner image for sticking a binding margin of a sheet are formed on an image carrier by toner image forming means. Then, a transfer bias is applied by a transfer means to a transfer area between the image carrier and the sheet to transfer the image toner image from the image carrier onto the sheet, thereby forming an image on the sheet. In addition, by applying a transfer bias to the transfer region by the transfer means, the sticking toner image is transferred from the image carrier onto the binding portion of the sheet, and the sticking force of the sticking toner image is used to transfer the sheet between the sheets. In the image forming system for adhering the binding margin, the toner image forming means uses the image forming conditions different from the image forming conditions for forming the image toner image to Form Kino the sticking toner image on said image bearing member at a high toner adhesion amount than the maximum toner amount per unit area formed by one, said transferring means, binding margin of the sheet the sticking toner image The transfer current that flows through the sticking toner image when transferring onto the image is greater than the transfer current that flows through the image toner image when transferring the image toner image having the maximum toner adhesion amount per unit area onto the sheet. The transfer bias is applied so as to increase.

  According to the present invention, a sticking toner image having a toner adhering amount exceeding the maximum toner adhering amount per unit area of an image formed by the image forming operation is attached to the binding portion of the sheet to obtain a larger adhering force. The excellent effect that it becomes possible is acquired.

1 is a schematic configuration diagram illustrating a printer that constitutes an image forming system according to an embodiment. FIG. 2 is a schematic configuration diagram illustrating a sheet post-processing device that constitutes the image forming system. It is a schematic block diagram of the binding process part in the paper post-processing apparatus. It is explanatory drawing which shows an example of the toner image for sticking in embodiment. FIG. 2 is a block diagram showing a part of an electric circuit in the printer. It is an expansion schematic diagram which shows a chevron patch. It is explanatory drawing for demonstrating the division obtained by dividing an image formation area. 6 is a flowchart illustrating an example of control for determining a target value of a primary transfer current in the embodiment. (A) And (b) is explanatory drawing which shows an example of the toner image formed on the intermediate transfer belt in order to demonstrate an average image area ratio. It is a graph which shows the relationship between the primary transfer voltage in the experiment which the present inventors conducted, the primary transfer current, and the test image. It is a graph which shows the relationship between the primary transfer rate in the same experiment, a primary transfer voltage, M toner reverse transfer rate, and a test image. It is a graph which shows the relationship between the primary transfer rate in the same experiment, a primary transfer current, M toner reverse transfer rate, and a test image. It is explanatory drawing which shows the other example of the toner image for sticking.

  Hereinafter, the present invention is a color printer (hereinafter simply referred to as “printer”) that forms a color image by a tandem type image forming unit as an image forming apparatus, and a sheet post-processing that is a sheet binding apparatus as a post-processing apparatus. An embodiment applied to an image forming system including an apparatus will be described.

First, a basic configuration of the printer in the embodiment will be described.
FIG. 1 is a schematic configuration diagram illustrating a printer according to the embodiment.
The printer 100 includes four process units 1Y, 1M, 1C, and 1Bk for yellow, magenta, cyan, and black (hereinafter referred to as Y, M, C, and Bk) as toner image forming means. The process units 1Y, 1M, 1C, and 1Bk use Y, M, C, and Bk toners of different colors as image forming substances for forming an image, but are otherwise configured in the same manner.

  Taking a process unit 1Y for generating a Y toner image as an example, this includes a photoreceptor 2Y, a developing device 3Y, a charging device, a photoreceptor cleaning device 5Y and the like as a unit held on a common holder. Are integrally attached to and detached from the printer main body.

  The charging device 4Y has a charging roller disposed so as to be in contact with or close to the photoreceptor 2Y, and the charging roller is rotationally driven by a driving unit (not shown). A predetermined charging bias is applied to the charging roller by a charging power source (not shown). Then, by generating a discharge between the charging roller and the photoreceptor 2Y, the surface of the photoreceptor 2Y is uniformly charged to the same polarity (for example, about −500 [V]) as the normal charging polarity of the toner. A scorotron charger or the like may be employed instead of such a charging device.

The photoreceptor 2Y is composed of a drum having a diameter of 30 [mm], the surface of which is coated with an organic photosensitive layer, and the capacitance is adjusted to 9.5 × 10 ⁻⁷ [F / m ² ]. Then, it is driven to rotate in the clockwise direction in the figure by a driving means (not shown). The surface of the photoreceptor 2Y uniformly charged by the charging device 4Y is exposed and scanned by a laser beam emitted from an optical writing unit 90 described later, and carries a Y electrostatic latent image.

  The developing device 3Y contains a developer (not shown) containing Y toner, which is a polyester-based polymer toner, and a magnetic carrier. An opening is formed in the casing of the developing device 3Y, and a part of the peripheral surface of the cylindrical developing sleeve is exposed from the opening and faces the surface of the photoreceptor 2Y. The developing sleeve carries the developer in the casing by a magnetic force generated by a magnet roller (not shown) fixed inside so as not to rotate with itself. Then, the developer is transported to a developing region where the developer and the photoconductor 2Y are opposed to each other in accordance with the rotation driving of the developer. In the developing region, a developing potential that moves Y toner of negative polarity from the sleeve side to the photosensitive member side acts between the developing bias applied to the developing sleeve and the electrostatic latent image on the photosensitive member 2Y. In addition, a non-image potential that moves Y toner of negative polarity from the photosensitive member side to the sleeve side acts between the developing sleeve and the background portion of the photosensitive member 2Y. The Y toner in the developer is transferred to the electrostatic latent image on the photoreceptor 2Y in the development area by the action of the development potential described above. As a result, the electrostatic latent image on the photoreceptor 2Y is developed into a Y toner image.

  The developing device 3Y has a toner density sensor (not shown) that measures the toner density of the internal developer. The detection result by the toner density sensor is sent to a control unit (not shown) as a voltage signal. The control unit includes a RAM, in which the target value of the output voltage from the toner density sensor is stored. Then, the value of the output voltage from the toner density sensor is compared with the target value, and the Y toner supply device (not shown) is driven for a time corresponding to the comparison result. By this driving, an appropriate amount of Y toner is supplied to the developer whose Y toner density is reduced by consumption of Y toner accompanying development. For this reason, the toner concentration of the developer in the developing device 3Y is maintained within a predetermined range. Similar toner supply control is performed for the developers in the developing devices 3M, 3C, 3Bk for other colors.

The Y process unit 1Y has been described in detail. The process units 1M, 1C, and 1Bk for other colors have the same configuration, and M, C, and Bk toner images are formed on the photoreceptors 2M, 2C, and 2Bk. It is formed. Development is performed by the developing devices 3Y, 3M, 3C, and 3Bk to form toner images of Y, M, C, and Bk. Note that the toner adhesion amount per unit area when a full-color image is formed on the photoreceptor is about 0.45 [mg / cm ² ].

  An optical writing unit 90 is disposed below the process units 1Y, 1M, 1C, 1Bk. The optical writing unit 90 as a latent image forming unit includes a laser diode (LD) type four light sources prepared for each color, a set of polygon scanners composed of a six-sided polygon mirror and a polygon motor, A lens such as an fθ lens and a long cylindrical lens arranged in the optical path of each light source and a mirror are provided. The optical writing unit 90 irradiates laser light L emitted based on image information from each light source, and scans the uniformly charged surfaces of the photoreceptors 2Y, 2M, 2C, and 2Bk. The potential of the laser exposure portion in the photoreceptors 2Y, 2M, 2C, and 2Bk is attenuated (for example, the residual potential during the entire surface exposure is attenuated to about −30 [V]), and the potential is lower than the surrounding background portion. It becomes a state. A portion in such a state becomes an electrostatic latent image of Y, M, C, and Bk. The optical writing unit 90 applies the laser light L emitted from the light source to the photoreceptors 2Y, 2M, 2C, and 2Bk via a plurality of optical lenses and mirrors while deflecting the laser light L by a polygon mirror that is rotationally driven by a motor. Irradiation. Instead of such a configuration, it is also possible to employ one that performs optical scanning with an LED array.

  Above the process units 1Y, 1M, 1C, and 1Bk, the endless intermediate transfer belt 21 is moved endlessly in the counterclockwise direction in the drawing, and the lower stretched surface is brought into contact with the photoreceptors 2Y, 2M, 2C, and 2Bk. A transfer unit 20 that is in contact with each other and forms a primary transfer nip for Y, M, C, and Bk is disposed. The Y, M, C, and Bk toner images formed on the photoreceptors 2Y, 2M, 2C, and 2Bk are primarily transferred while being superimposed on the intermediate transfer belt 21 at the primary transfer nip of each color.

  The transfer residual toner adhering to the surfaces of the photoreceptors 2Y, 2M, 2C, and 2Bk after passing through the primary transfer nips for Y, M, C, and Bk is removed by the photoreceptor cleaning devices 5Y, 5M, 5C, and 5Bk. It is removed from the surface of the photoreceptor.

  A paper feed cassette 95 is disposed below the optical writing unit 90. In the paper feed cassette 95, a plurality of paper sheets P as recording materials, which are sheets, are stored in a bundle of paper sheets. A paper feed roller 95a is in contact with the uppermost paper sheet P. Yes. When the paper feed roller 95a is driven to rotate counterclockwise in the figure by a driving means (not shown), the uppermost paper P in the paper feed cassette 95 extends in the vertical direction on the right side of the cassette in the figure. The paper is discharged toward the disposed paper feed path. The paper P sent to the paper feed path is conveyed from the lower side to the upper side in the figure. The process linear velocity, which is the linear velocity of the photoreceptors 2Y, 2M, 2C, 2Bk and the intermediate transfer belt 21, is set to 120 [mm / sec].

  A registration roller pair 32 is disposed at the end of the paper feed path. The registration roller pair 32 temporarily stops the rotation of both rollers as soon as the sheet P is sandwiched between the rollers. Then, the paper P is sent out toward a secondary transfer nip described later at an appropriate timing.

  The transfer unit 20 disposed above the process units 1Y, 1M, 1C, and 1Bk includes the intermediate transfer belt 21, the primary transfer rollers 25Y, 25M, 25C, and 25Bk, and the driven roller 23 disposed in the belt loop. And a secondary transfer counter roller 24. Further, it also has a secondary transfer roller 26 and a belt cleaning device 28 disposed in the belt loop.

The intermediate transfer belt 21 as a nip forming member is an endless belt with a thickness of 80 [μm] having a belt base made of conductive polyamideimide resin in which carbon is dispersed, and its volume resistivity is 1 × 10 ⁹ [ Ω · cm] (value measured under a voltage application condition of 100 V with a Hirester UP MCP HT450 manufactured by Mitsubishi Chemical). Then, in a state of being stretched around each of the rollers disposed in the belt loop, it is moved endlessly in the counterclockwise direction in the figure by the rotational drive of at least one of the rollers.

The four primary transfer rollers 25Y, 25M, 25C, and 25Bk are arranged so as to press the endlessly moving intermediate transfer belt 21 against the photoreceptors 2Y, 2M, 2C, and 2Bk. Thus, primary transfer nips for Y, M, C, and Bk where the intermediate transfer belt 21 and the photoreceptors 2Y, 2M, 2C, and 2Bk are in contact are formed. The primary transfer rollers 25Y, 25M, 25C, and 25Bk are obtained by providing a conductive sponge roller portion made of a resin in which an ionic conductive agent is dispersed on the peripheral surface of a metal rotating shaft member. The volume resistivity of the conductive sponge roller portion is about 5 × 10 ⁸ [Ω · cm]. The metal rotating shaft member is disposed at a position shifted by 3 [mm] on the downstream side in the belt moving direction with respect to the rotating shaft of the photosensitive member.

  The primary transfer rollers 25Y, 25M, 25C, and 25Bk are applied with a primary transfer bias having a polarity opposite to the charging polarity of the toner by the primary transfer power supplies 81Y, 81M, 81C, and 81Bk. As a result, a transfer electric field that draws the toner image on the photoconductor from the photoconductor side to the belt side is formed in the primary transfer nip. The intermediate transfer belt 21 sequentially passes through the primary transfer nips for Y, M, C, and Bk along with the endless movement thereof, and the photoreceptors 2Y, 2M, 2C, The Y, M, C, and Bk toner images on 2Bk are superimposed and primarily transferred. As a result, a four-color superimposed toner image (hereinafter referred to as “four-color toner image”) is formed on the intermediate transfer belt 21.

  The secondary transfer counter roller 24 disposed on the inner side of the belt loop is disposed so that the intermediate transfer belt 21 is sandwiched between the secondary transfer roller 26 disposed on the outer side of the belt loop. Thus, a secondary transfer nip where the front surface of the intermediate transfer belt 21 and the secondary transfer roller 26 abut is formed on the right side of the belt in the drawing. The registration roller pair 32 described above sends the paper P sandwiched between the rollers toward the secondary transfer nip at a timing at which the paper P can be synchronized with the four-color toner image on the intermediate transfer belt 21.

  A secondary transfer bias having a polarity opposite to that of the toner is applied to the secondary transfer roller 26. The four-color toner images on the intermediate transfer belt 21 are secondarily transferred collectively onto the paper P in the secondary transfer nip by the action of the secondary transfer bias and nip pressure. Then, combined with the white color of the paper P, a full color toner image is obtained.

  Untransferred toner that has not been transferred to the paper P adheres to the intermediate transfer belt 21 after passing through the secondary transfer nip. This is cleaned by the belt cleaning device 28. The belt cleaning device 28 has a cleaning roller in contact with the front surface of the intermediate transfer belt 21, and removes residual toner on the belt by electrostatic transfer to the cleaning roller.

  A fixing device 40 is disposed above the secondary transfer nip. The fixing device 40 forms a fixing nip by abutting a fixing roller 41 containing a heat source such as a halogen lamp and a pressure roller 42 pressed toward the fixing roller 41. The paper P that has passed through the secondary transfer nip is separated from the intermediate transfer belt 21 and then sent into the fixing device 40. Then, in the process of being conveyed from the lower side to the upper side in the figure while being sandwiched by the fixing nip in the fixing device 40, the full color toner image is fixed by being heated or pressed by the fixing roller 41.

FIG. 2 is a schematic configuration diagram illustrating the sheet post-processing device 50 according to the embodiment.
The paper P on which the fixing process has been performed in the printer 100 exits the fixing device 40 and is sent to the paper post-processing device 50 through a pair of paper discharge rollers (not shown). The sheet post-processing device 50 includes a binding processing unit 60 that performs a binding process on the sheet bundle PT in which the sheets P conveyed from the printer 100 via the inlet 51 are bundled. In addition, a paper discharge unit 58 on which the paper P or the paper bundle PT is discharged and stacked is provided. The sheet post-processing device 50 is detachably installed on the printer 100.

  The paper P discharged from the printer 100 is conveyed from the inlet 51 into the paper post-processing device 50. When the “normal processing mode” is previously input by the user to the operation panel (not shown) of the printer 100, the paper P is discharged via the straight conveyance path 55 by switching the conveyance path by the switching claw 52. The paper is discharged to the section 58 as it is. On the other hand, when the “binding processing mode” is input in advance on the operation panel by the user, the sheet P is loaded via the processing transport path 53 by switching the transport path by the switching claw 52. It is conveyed toward. Then, when a predetermined number of sheets P are stacked and stocked in the stacking unit 61 to form a desired sheet bundle PT, alignment processing in the width direction and the conveyance direction of the sheet bundle PT is performed by the movement of the unillustrated jigyoga fence. Done. Thereafter, the binding processing unit 60 performs binding processing on the sheet bundle PT, and after the binding processing is performed, the sheet bundle PT is transported by the transport roller 56 and the transport belt 54 and then discharged to the paper discharge unit 58. Paper.

FIG. 3 is a schematic configuration diagram of the binding processing unit 60.
The binding processing unit 60 of the present embodiment is formed so as to perform binding processing on the sheet bundle PT using an adhesive force of toner without using a metal needle.
As shown in FIG. 3, the binding processing unit 60 is provided with a stacking unit 61 on which a plurality of sheets P with a toner image fixed are stacked as a sheet bundle PT. When the paper P on which an image is formed through the image forming process in the printer 100 and the fixing process in the fixing device 40 is conveyed to the paper post-processing device 50, the paper P is positioned one by one in the abutting portion 61a on the front end side of the paper. In the state where the binding margin A to be abutted, the stacking unit 61 is loaded.

  Here, in the binding portion A (portion surrounded by a broken line in FIG. 3) of the paper P stacked on the stacking unit 61, a sticking toner for adhering the papers P apart from the image toner image. The image is fixed. This sticking toner image is formed through an image forming process in the image forming unit 4 in the printer 100 and a fixing process in the fixing device 40 in the same manner as the image toner image. In the present embodiment, out of a plurality of sheets P formed as a sheet bundle PT, sheets on the surface (image recording surface) of the second and subsequent sheets P excluding the sheet P first stacked on the stacking unit 61. A sticking toner image is formed on the binding margin A set on the leading end side in the transport direction. The details of the sticking toner image will be described later.

  Further, the binding processing unit 60 is provided with a pressing unit 63 that applies pressure to the binding portion A of the sheet bundle PT and a receiving unit 62 that receives the pressing force of the pressing unit 63. Each of the pressurization unit 63 and the receiving unit 62 is provided with heaters 72 and 73 as heating means. Moreover, heat sinks 64 and 65 as cooling means are also provided in the pressurizing unit 63 and the receiving unit 62, respectively.

  The receiving portion 62 is fixed to the lower portion of the stacking portion 61 so as to face the binding portion A of the sheet bundle PT stacked on the stacking portion 61. The pressing unit 63 is disposed at a position facing the receiving unit 62 via the binding portion A of the sheet bundle PT stacked on the stacking unit 61. The pressurizing unit 63 is configured to be relatively movable in a direction in which the pressurizing unit 63 contacts and separates from the receiving unit 62.

  Specifically, the pressurizing unit 63 is movable so as to be slidable between the direction approaching and moving away from the receiving unit 62 guided by the guide rail 67 along the arrow direction in FIG. It is fixed on the plate 68. The movable plate 68 is connected to a tension spring 69 that urges the movable plate 68 in a direction away from the receiving portion 62 (sheet bundle PT). When the eccentric cam 66 is separated from the movable plate 68, the movable plate 68 is placed on a stopper portion (not shown) installed at a position sufficiently away from the receiving portion 62 of the guide rail 67 by the urging force of the tension spring 69. Positioned at the abutting position. On the other hand, when the eccentric cam 66 is driven to rotate about the rotation shaft portion by a drive motor (not shown), the movable plate 68 is moved toward the receiving portion 62 by the eccentric cam 66 so as to resist the urging force of the tension spring 69. It is pushed and moves in a direction approaching the receiving part 62. As a result, the pressurizing unit 63 moves to the receiving unit 62 side and sandwiches and presses the binding portion A of the sheet bundle PT with the receiving unit 62.

  Simultaneously with this pressurization, the toner images to be stuck on the binding margin A in the sheet bundle PT are heated by the heaters 72 and 73 provided in the receiving part 62 and the pressing part 63. Thus, the sticking toner image is melted in a pressurized state, and the sticking toner image is solidified by subsequent natural cooling, whereby the sheets are bonded to each other, and the sheet bundle PT is bound. In this embodiment, every time a predetermined plurality of sheets P forming the sheet bundle PT are stacked on the stacking unit 61, the operation of repeatedly performing the binding process (pressing / heating process) once is performed. ing.

  The moving mechanism that moves the pressing portion 63 in the direction approaching and moving away from the receiving portion 62 is, for example, a compression spring that urges the movable plate 68 in the approaching direction and an eccentricity that pushes the movable plate 68 in the moving away direction. You may comprise with the cam 66. FIG. A linear actuator may be used as the moving mechanism. The heaters 72 and 73 provided in the pressurizing unit 63 and the receiving unit 62 can use heat sources such as a ceramic heater, a resistance heating element, a halogen heater, and an electromagnetic induction coil. The heaters 72 and 73 are heated and controlled so that the receiving part 62 and the pressing part 63 reach a temperature equal to or higher than the melting point of the toner image to be stuck. Since the receiving part 62 and the pressurizing part 63 are heated when the heat of the heaters 72 and 73 is conducted, it is preferable to form the receiving part 62 and the pressing part 63 with a highly thermally conductive material such as a metal material.

  In addition, a surface layer (not shown) is formed at a portion of the pressurizing unit 63 that contacts the sheet bundle. The surface layer has a two-layer structure. The first layer in contact with the sheet bundle is formed of a low friction material such as a fluororesin material in order to prevent the sheet P and toner from adsorbing to the pressure unit. The second layer stacked on the first layer is for adjusting the pressing force when the binding portion A of the sheet bundle PT is sandwiched between the pressurizing unit 63 and the receiving unit 62, and is a rubber material or the like. Made of elastic material.

  Further, the receiving portion 62 also has a surface layer having the same configuration as that of the pressing portion 63. That is, a first layer formed of a low friction material such as a fluororesin material and a second layer formed of an elastic material such as a rubber material. Since the surface layers of the pressurizing unit 63 and the receiving unit 62 are to conduct heat of the heaters 72 and 73 to the binding portion A and heat them, it is preferable to form the surface layer with a highly heat conductive material.

Next, features of the present embodiment will be described.
In order to bind the paper with a strong sticking force, it is effective to increase the amount of toner attached per unit area attached to the binding margin A. For example, as shown in FIG. 4, the sticking toner image is formed in a belt-like pattern having a certain width d. In the example of the sticking toner image shown in FIG. 4, the width in the main scanning direction (vertical direction in the figure) is 282 mm (image area ratio is 95%), and the width d in the sub-scanning direction (horizontal direction in the figure) is 5 mm. It is. The amount of toner adhered per unit area of the sticking toner image T was the same as that of the solid image for image formed on the image portion on the paper P. The image solid toner image here is an image toner image to which the maximum toner adhesion amount per unit area is adhered. More specifically, it is an image toner image formed with a toner adhesion amount per unit area set to obtain the maximum image density in the printer 100. In the present embodiment, the toner adhesion amount (maximum toner adhesion amount) per unit area of the solid image for image on the photoreceptor is set to about 0.45 [mg / cm ² ].

In the printer 100, the toner adhesion amount per unit area is adjusted by appropriately adjusting the toner image forming conditions (charging conditions of the charging device, exposure conditions of the optical writing unit 90, developing conditions of the developing device 3, etc.). It is also possible to form a toner image exceeding the maximum toner adhesion amount. However, regarding the image toner image, even if the toner adhesion amount per unit area exceeds the above-described maximum toner adhesion amount (0.45 [mg / cm ² ]), a substantial change occurs in the obtained image density. Therefore, adhering toner exceeding the maximum toner adhering amount leads to wasteful consumption of toner. In the present embodiment, as the image forming condition for the sticking toner image T, a condition different from the image forming condition of the image toner image is used, and the sticking toner having a larger toner adhesion amount per unit area than the image solid toner image. By forming an image on the photoreceptor 2Bk and finally transferring it to the binding portion A of the paper P, a strong sticking force is obtained.

In this embodiment, the sticking toner image is formed only by the Bk process unit 1Bk, and the other process units 1Y, 1M, and 1C are described as not forming sticking toner images. A process unit having a color different from 1Bk may be used, or a sticking toner image formed by two or more process units may be used in an overlapping manner. In the present embodiment, the developing voltage (image forming condition) applied to the developing sleeve in the developing device 3Bk when developing the sticking toner image is changed between the developing process for the image toner image and the developing process for the sticking toner image. To do. Specifically, the development voltage during the development processing of the image toner image is set to −350 [V], whereas the development voltage during the development processing of the sticking toner image is set to −500 [V]. The Due to the difference in the development voltage, the toner adhesion amount per unit area in the solid image for image is about 0.45 [mg / cm ² ], whereas the toner adhesion amount per unit area in the solid toner image to be attached is approximately 0.45 [mg / cm ² ]. Is about 0.65 [mg / cm ² ].

  Here, the sticking toner image T having a toner adhesion amount per unit area larger than that of the solid image for image is finally transferred and adhered to the binding portion A of the paper P from the photosensitive member. If the transfer conditions (primary transfer conditions and secondary transfer conditions) are the same as those for the solid toner image, the transfer rate may be poor and a sufficient amount of toner may not be adhered to the binding portion A of the paper P. Specifically, if a transfer current larger than the transfer current at the time of transferring the image solid toner image is not passed, the sticking toner image having a larger amount of toner adhesion per unit area than the image solid toner image is close to the image solid toner image. Alternatively, a similar transfer rate cannot be obtained.

  Therefore, in the present embodiment, the primary transfer roller is configured such that the transfer current flowing through the sticking toner image T during the primary transfer is larger than the transfer current flowing through the solid image for image during the primary transfer of the solid image for image. The primary transfer bias applied to 25 Bk is controlled.

FIG. 5 is a block diagram showing a part of an electric circuit in the printer.
In the figure, a control unit 200 as a control means includes a CPU (Central Processing Unit) 200a as a calculation means, a RAM (Random Access Memory) 200c as a nonvolatile memory, a ROM (Read Only Memory) 200b as a temporary storage means, and the like. ing. The control unit 200 controls the entire apparatus, and various devices and sensors are connected. In the figure, only a part of these devices is shown. The control unit 200 controls driving of each device based on a control program stored in the RAM 200c or the ROM 200b. Further, the primary transfer current value of Y, M, C, and Bk is determined based on a write signal at the time of exposure generated from image information sent from an external personal computer or the like, and becomes the determined primary transfer current value. In this manner, the primary transfer power supplies 81Y, 81M, 81C, 81Bk for Y, M, C, Bk are controlled. The control unit 200 functions as a transfer current control unit together with the primary transfer power supplies 81Y, 81M, 81C, 81Bk. The target value of the primary transfer current output from the primary transfer power supplies 81Y, 81M, 81C, 81Bk is output as a PWM signal from the control unit 200 and input to the primary transfer power supplies 81Y, 81M, 81C, 81Bk.

  Further, the control unit 200 performs a positional deviation amount correction process immediately after a main power switch (not shown) is turned on or whenever a predetermined number of prints are performed. In this misregistration amount correction process, misregistration detection images made up of a plurality of toner images called chevron patches PV as shown in FIG. 6 are formed on the intermediate transfer belt 21. The optical sensor unit 86 shown in FIG. 5 passes the light emitted from the light emitting means through the condensing lens, reflects it on the surface of the intermediate transfer belt 21, and receives the reflected light by its own light receiving means. Outputs voltage according to the amount. When the toner image in the chevron patch PV formed on the intermediate transfer belt 21 passes directly below the optical sensor unit 86, the amount of light received by the light receiving means of the optical sensor unit 86 changes greatly. Accordingly, the control unit 200 can detect each toner image in the chevron patch PV formed on the intermediate transfer belt 21. As described above, the optical sensor unit 86 functions as an image detection unit in combination with the control unit 200. As the light emitting means, an LED or the like having an amount of light that can generate reflected light necessary for detecting a toner image is used. As the light receiving means, a CCD having a large number of light receiving elements arranged in a straight line is used.

  The controller 200 detects each toner image in the chevron patch PV formed on the intermediate transfer belt 21, thereby detecting a position in the sub-scanning direction (belt moving direction) in each toner image. As shown in FIG. 6, the chevron patch PV is a posture in which the toner images of each color of Y, M, C, and Bk are inclined by about 45 ° from the main scanning direction (the direction in which the laser beam scans on the surface of the photoreceptor). The line pattern group is arranged at a predetermined pitch in the belt moving direction which is the sub-scanning direction. For such Y, C, M toner images in the chevron patch PV, the difference in detection time from the Bk toner image is read. In the figure, the vertical direction of the drawing corresponds to the main scanning direction, and after the Y, M, C, and Bk toner images are arranged in order from the left, Bk, C, M and Y toner images are further arranged. Based on the difference between the actual measurement value and the theoretical value of the detection time differences tky, tkc, and tkm with respect to Bk as the reference color, the amount of deviation in the sub-scanning direction of each color toner image, that is, the amount of positional deviation is obtained. Then, based on the misregistration amount, the optical writing start timing for the photoconductor of the optical writing unit (not shown) is corrected, and the misregistration of each color toner image due to the speed fluctuation of the photoconductor and the intermediate transfer belt 21 is corrected. Reduce.

  Primary transfer power supplies 81Y, 81M, 81C, and 81Bk for applying a transfer bias to the intermediate transfer belt 21 via primary transfer rollers 25Y, 25M, 25C, and 25Bk for Y, M, C, and Bk are respectively predetermined. A transfer current having the same value as the target value is output. The target values of the transfer currents output from the primary transfer power supplies 81Y, 81M, 81C, 81Bk are respectively on the photoconductor at the transfer nip (more specifically, in the configuration of the present embodiment, at the transfer nip outlet and its vicinity). This is determined based on the image area ratio in the main scanning direction of the image forming area.

  Specifically, the surface of the photoconductor is divided (divided) into 10 pixel sections as shown in FIG. 7 with reference to the leading edge of the image forming area in the sub-scanning direction (photoconductor surface moving direction). ) Is made. Therefore, each section includes 10 pixel lines each consisting of a set of pixels arranged in a straight line in the main scanning direction. Then, for each pixel line, the ratio of the number of pixels of the image portion to the total number of pixels (image area ratio of each pixel line) is obtained, and the average value of the ratios of the ten pixel lines included in each section (each The average image area ratio of the section) is acquired as the image area information of each section.

  In the present embodiment, the target value of the primary transfer current that flows when the image forming area corresponding to each section passes through the outlet of the primary transfer nip is determined according to the image area information of the corresponding section (image area ratio of the section). To decide. As a result, the primary transfer power supplies 81Y, 81M, 81C, and 81Bk allow the same transfer current to flow while the image forming area corresponding to each section passes through the exit of the primary transfer nip. Output voltage value (primary transfer bias) is adjusted. When the image forming area point corresponding to the most downstream end of the section passes through the transfer nip outlet, the target values of the primary transfer power supplies 81Y, 81M, 81C, 81Bk correspond to the image area information (image area ratio) of the next section. Will be changed. By such control, the waveform of the transfer current changes in a substantially rectangular wave like the graph shown in the lower part of FIG. That is, every time the intermediate transfer belt 21 and each of the photosensitive members 2M, 2C, and 2Bk move by 10 pixels in the sub-scanning direction, the primary transfer current flowing through the primary transfer rollers 25Y, 25M, 25C, and 25Bk is transferred to the primary transfer at that time. It changes to an optimum primary transfer current value corresponding to the image area ratio of the section corresponding to the image forming region portion passing through the nip exit.

FIG. 8 is a flowchart showing an example of control for determining the target value of the primary transfer current in this embodiment.
In this control example, when setting the target value of the primary transfer current of the corresponding color based on the writing signal of each color used in the optical writing unit 90, the leading edge of each image forming area (each page) is used as a reference. Count pixel lines. First, when writing data is generated (S1), the control unit 200 calculates the number of partitions (division size N) for the image from the image size information in the sub-scanning direction (S2). This division size N is, for example, a quotient value obtained by dividing the number of pixels in the sub-scanning direction of the image by a predetermined number of pixels in the sub-scanning direction (10 pixels in this control example) constituting each section. Calculated by adding 1.

  Next, the count value indicating the number of sections X is initialized to zero (S3), and the count value indicating the number of pixel lines (number of pixels in the sub-scanning direction) A is initialized to zero (S4). Then, after incrementing the count value of the number A of pixel lines by one (S5), the image area ratio for the Ath pixel line is calculated (S6). The image area ratio is calculated using an image input signal (image information) input from a personal computer, a scanner, or the like, or a writing signal of each color used in the optical writing unit 90.

  When the image area ratio is calculated for each of the first to tenth pixel lines in this manner (Yes in S7), the average image area ratio is calculated (S8). In this control example, this average image area ratio is used as image area information for the section X including the first to tenth pixel lines, and the control unit 200 follows the transfer current target value calculation algorithm stored in the RAM 200c. Then, the target value I (X) of the primary transfer current corresponding to the section X is calculated (S9, S10). This algorithm shows the relationship between the average image area ratio and the optimum primary transfer current value, and is determined in advance by experiments or simulations.

In this way, the optimum primary transfer current target values I (1) to I (N) are set for the first to Nth sections divided into N for one image forming area.

  In the present embodiment, the target value of the primary transfer current at that time is determined on the basis of the image area ratio of the image forming region portion passing through the primary transfer nip exit for the reason described below. That is, in the configuration of the present embodiment, most of the primary transfer current flowing between the photosensitive members 2Y, 2M, 2C, and 2Bk and the intermediate transfer belt 21 is transferred to the photosensitive members 2Y, 2M, 2C, and 2Bk and the intermediate transfer belt. This is due to peeling discharge between the two at the exit of the primary transfer nip where the belt 21 is separated from each other. At the primary transfer nip exit, even though the amount of current supplied from the primary transfer power supplies 81Y, 81M, 81C, 81Bk is relatively small, the image area ratio of the image forming region portion passing therethrough is relatively low. Most of the current supplied from the primary transfer power source is used for the peeling discharge between the non-image portion (background portion) of the photoreceptor and the intermediate transfer belt. For this reason, almost no current flows through the image portion of the photosensitive member, and a transfer failure occurs.

  In this embodiment, since the primary transfer current can flow according to the image area ratio of the image forming area portion passing through the primary transfer nip exit, what image area ratio is required for the image forming area portion passing through the primary transfer nip exit. Even in such a case, a required amount of primary transfer current can be supplied to the image portion. As a result, it is possible to realize a stable transfer rate that does not cause transfer defects for images having any image area ratio.

Next, an image area ratio that is image area information of each section X used for controlling the primary transfer current will be described with reference to FIGS.
FIGS. 9A and 9B are explanatory diagrams illustrating an example of a toner image formed on the intermediate transfer belt 21.
The average image area ratio of a section is an average value of the image area ratio of each of ten pixel lines included in the section. The image area ratio of each pixel line is the image portion (toner) on one pixel line (one pixel in the sub-scanning direction) over the width W of the image forming area of the intermediate transfer belt 21 in the main scanning direction (left-right direction in FIG. 9). This is a numerical value obtained by dividing the portion to which the is attached by the entire area of the pixel line.

  For example, the toner image shown in FIG. 9A has only one image portion composed of a strip-shaped solid image extending in the sub-scanning direction, and the width in the main scanning direction is the image forming region width W ×. It is 0.1 [mm]. In this case, the average image area ratio of the section including the belt-like solid image is 10 [%]. On the other hand, as shown in FIG. 9B, in the case of a toner image in which a plurality of image portions are distributed in the sub-scanning direction, the calculation is based on the total area of these image portions.

Next, an experiment conducted by the inventor will be described.
The inventor prepared a printer testing machine having the same configuration as the printer according to the embodiment shown in FIG. In this printer testing machine, an experiment was conducted in which three types of test images were output to examine the relationship between the primary transfer current, the primary transfer voltage, the primary transfer rate, and the reverse transfer rate. Specifically, as one of the three types of test images, the length in the main scanning direction is 14.85 [mm] and extends over the entire area in the sub scanning direction along the length direction of the A4 size paper. An existing strip-shaped Bk 5% test image (image area ratio 5%) was printed. For the output voltage from the primary transfer power supply 81Bk for Bk, constant voltage control for outputting a constant voltage was performed. The voltage control target value was gradually increased from 1000 [V] to 2300 [V] every 100 [V], and a Bk 5% test image was printed at each control target value. In each print, the output current value from the primary transfer power supply 81Bk for Bk was measured. Further, the toner adhesion amount per unit area for the Bk 5% test image on the Bk photoconductor 2Bk before entering the Bk primary transfer nip, and the toner adhesion per unit area on the photoconductor 2Bk after passing through the primary transfer nip. The amount was measured. The ratio of the former toner adhesion amount minus the latter toner adhesion amount to the former was determined as the primary transfer rate.

  As another one of the three types of test images, a Bk 100% test image (image area ratio 100%) adhered to the entire surface of A4 size paper was printed. As another example, an M100% + Bk5% test image obtained by overlaying a Bk5% test image on an M100% test image adhering to the entire surface of A4 size paper was printed. As with the Bk 5% test image, these test images are gradually increased from 1000 [V] to 2300 [V] every 100 [V], and the primary transfer current value and the primary transfer rate under each condition. And measured. Also, for the M100% + Bk5% test image, the amount of M toner adhered to the background portion of the photoreceptor 2Bk after passing through the primary transfer nip for Bk is measured, and the measurement result is the amount at the time of entering the nip. The M toner reverse transfer rate was determined. The toner adhesion amount was measured based on the spectroscopic measurement result by a reflection spectral densitometer X-Rite 938.

  FIG. 10 is a graph showing the relationship between the primary transfer voltage, the primary transfer current, and the test image in this experiment. FIG. 11 is a graph showing the relationship between the primary transfer rate, the primary transfer voltage, the M toner reverse transfer rate, and the test image in this experiment. FIG. 12 is a graph showing the relationship between the primary transfer rate, the primary transfer current, the M toner reverse transfer rate, and the test image in this experiment.

  As shown in FIG. 11, when a single color toner image consisting only of Bk is formed as a test image (Bk 5%, Bk 100%), the primary transfer voltage exceeds a predetermined value regardless of the image area ratio. The primary transfer rate begins to drop sharply. More specifically, when the primary transfer voltage exceeds 2000 [V], the primary transfer rate starts to rapidly decrease. Under the condition of 2000 [V], as shown in FIG. 10, the current flowing through the primary transfer nip varies depending on the image area ratio. Specifically, in the case of a Bk 5% test image, a primary transfer current of 30 [μA] is output from the primary transfer power supply 81Bk under the condition of the primary transfer voltage = 2000 [V], whereas the Bk 100% test image In this case, a primary transfer current of 21 [μA] is output from the primary transfer power supply 81Bk under the condition of primary transfer voltage = 2000 [V].

As described above, when the primary transfer bias is controlled at a constant voltage, the primary transfer current flows as the image area ratio on the photosensitive member decreases. The reason is that, under the condition of constant voltage control in which the primary transfer voltage is controlled to be constant, the lower the image area ratio, the larger the charge amount of the photoconductor and the more current flows between the belt and the photoconductor. Because. For example, in the printer testing machine, the Bk photoconductor 2Bk is uniformly charged to about −500 [V] by the charging device 4Bk. For the image portion (electrostatic latent image), the potential which was −500 [V] is attenuated to about −30 [V] by irradiation with the laser beam L. Since the photoconductor 2Bk having a capacitance of 9.5 × 10 ⁻⁷ [F / m ² ] is used, the area charge density of the background portion of the photoconductor 2Bk is about −475 [μC / m. ² ] grade. On the other hand, the area charge density of the image portion of the photosensitive member 2Bk is the toner charge amount 0.45 × 10 ⁻³ [g / cm ² ] × −20 [μC / g] = − 0.009 [μC / cm ² ]. = −90 [μC / m ² ] and the charge amount (−29 [μC / m ² ]) of the residual potential (about −30 [V]) of the photosensitive member, about −119 [μC / m m ² ]. In the photoreceptor 2Bk, the amount of charge in the background portion is four times or more that in the image portion. For this reason, in the primary transfer nip, the electric field formed between the background portion of the photoreceptor 2Bk and the intermediate transfer belt 21 rather than the electric field formed between the image portion of the photoreceptor 2Bk and the intermediate transfer belt 21. Is stronger. Then, as the image area ratio of the photosensitive member 2Bk decreases, the current easily flows between the belt and the photosensitive member. Therefore, the amount of output current increases in order to set the voltage output value from the primary transfer power supply 81Bk to a predetermined value. It becomes.

  As described above, in the constant voltage control, the output current value from the power source increases as the image area ratio decreases. However, even if the image area ratio is the same, the output current value varies greatly depending on the environment. This is because when the environment changes, the resistance values of the intermediate transfer belt 21 and the primary transfer roller 25Bk change accordingly. For this reason, under constant voltage control conditions, even if the target value of the output voltage is changed according to the image area ratio, the primary transfer current may become excessive or insufficient depending on the environment, resulting in a transfer failure. May cause. For this reason, the primary transfer bias is more advantageously controlled by constant current rather than constant voltage control. In addition, it is desirable to change the target value of the output current according to the image area ratio, instead of simple constant current control.

  In the primary transfer nip for Y, for the reason described below, it is desirable to employ a value that provides the highest possible transfer efficiency as the target value of the primary transfer current. That is, the Y toner image sequentially passes through all the primary transfer nips for M, C, and Bk, and each time, although slightly, the toner adheres to the photoreceptor and is lost. This is because they tend to be thinner than other color toner images. Therefore, for the target value of the output current from the primary transfer power supply 81Y for Y, it is desirable to increase the output voltage to a value that provides the maximum transfer efficiency. This experiment is performed in an environment of 25 [° C.], and the maximum transfer efficiency is obtained under the condition that the primary transfer voltage is 2000 [V]. Under this condition, a primary transfer current of 30 [μA] flows in the Bk 5% test image as shown in FIG. 10, whereas a primary transfer current of 21 [μA] flows in the Bk 100% test image. In simple constant voltage control, when the room temperature changes from 25 [° C.] and the resistance of the belt or roller changes, even if the primary transfer voltage is maintained at 2000 [V], the primary transfer current becomes excessive. Or lack. The value of 2000 [V] is a voltage condition for obtaining the maximum transfer efficiency in an environment of 25 [° C.]. When the room temperature is changed from 25 [° C.], the voltage condition for realizing the maximum transfer efficiency is also changed. Because it will end up. On the other hand, the current condition for obtaining the maximum transfer efficiency is constant regardless of the environment. Specifically, when the image area ratio is 5%, the maximum transfer efficiency can be realized by maintaining the primary transfer current value constant at 30 [μA] regardless of the environment. When the image area ratio is 100%, the maximum transfer efficiency can be realized by maintaining the primary transfer current value constant at 100 = 21 [μA] regardless of the environment.

  As described above, with regard to the primary transfer power source 81Y for Y, the maximum transfer efficiency can be maintained by changing the target value of the output current in accordance with the image area ratio. However, if the same constant current control is performed also with the primary transfer power supplies 81M, C, and Bk for M, C, and Bk, the Y toner on the belt is transferred to the photoreceptors 2M, C at the primary transfer nip for M, C, and Bk. , Bk is easily transferred back to the background.

  For example, as shown in FIG. 11 described above, in the primary transfer nip for Bk, depending on the value of the primary transfer voltage, the reverse transfer rate of the M100% toner image on the belt to the photoreceptor 2Bk background portion ( M toner reverse transfer rate) becomes very high. Specifically, the M toner reverse transfer rate remains below 0.01 [%] under the condition where the primary transfer voltage is set to 1000 to 1500 [V], but the primary transfer voltage is higher than 1600 [V]. Then, it can be seen that the M toner reverse transfer rate starts to increase rapidly.

  On the other hand, when the primary transfer voltage exceeds 2000 [V], the reason why the transfer efficiency starts to rapidly decrease is considered as follows. That is, when the primary transfer voltage exceeds 2000 [V], the potential difference between the image portion of −30 [V] on the photoreceptor and the intermediate transfer belt 21 exceeds the discharge start voltage. Then, in the primary transfer nip, discharge is actively generated between the image portion (-30 [V]) of the photoreceptor and the intermediate transfer belt 21, and the toner on the image portion is reversely charged by the discharge. End up. This reverse charging causes the toner on the image area to remain on the image area without being electrostatically moved onto the intermediate transfer belt 21, which is considered to be a cause of a decrease in transfer efficiency.

  When such a decrease in transfer efficiency occurs, within the primary transfer nip, not only between the −30 [V] image portion of the photoreceptor and the belt, but also the −500 [V] background portion of the photoreceptor. There is also a discharge between the belt and the belt. However, when printing a single color image, the toner image on the photoconductor is transferred to the intermediate transfer belt 21 in which no toner image exists in the primary transfer nip. No toner is interposed between them. For this reason, the discharge between the background portion and the belt does not appear as a prominent phenomenon. Focusing on the image portion (−30V) of the photosensitive member in which a significant phenomenon of transfer efficiency is reduced, if the output voltage from the primary transfer power supply is larger than 2000 [V], the image portion between the photosensitive member and the belt Is made larger than the discharge start voltage. Since it is difficult to grasp the surface potential of the belt, for the sake of convenience, considering the output voltage from the primary transfer power supply, in this experiment, if the potential difference between the output voltage and the photosensitive member is larger than 2030 [V], the photosensitive This means that the potential difference between the body and the belt is larger than the discharge start voltage.

  As described above, in this experiment, when the output voltage from the primary transfer power supply 81Bk for Bk is made larger than 1600 [V], the M toner reverse transfer rate starts to rapidly increase. The cause of such a rapid increase is considered as follows. That is, when printing a multi-color image by superimposing two or more colors instead of a single-color image, the toner image already transferred onto the belt in the primary transfer nip after the second color is transferred to the subsequent photoreceptor. Intervene between the background and the belt. At this time, if the potential difference between the background portion (−500 [V]) of the photoconductor and the output voltage from the primary transfer power supply is larger than 2030 [V], discharge occurs between the background portion and the intermediate transfer belt 21. Occur. Then, the toner in the toner image that has already been transferred onto the intermediate transfer belt 21 is reversely charged by the discharge and reversely transferred to the background portion of the photoreceptor. Since the potential of the background portion of the photoreceptor is about −500 [V], if the output voltage from the primary transfer power supply is larger than 1530 [V], such reverse transfer is caused. In this experiment, since the output voltage is increased in units of 100 [V], 1530 [V] corresponds to the condition of 1600 [V]. Therefore, in the graph shown in FIG. 9, when the primary transfer voltage exceeds 1600 [V], it is considered that the M toner reverse transfer rate starts to increase rapidly.

  Under the condition of room temperature 25 [° C.], as described above, the primary transfer voltage is 5% for the primary transfer current = 30 [μA] and the 100% image is for the primary transfer current 21 [μA]. Becomes about 2000 [V] at which the maximum transfer efficiency can be realized. It is assumed that such primary transfer current control is adopted not only by the primary transfer power supply 81Y for Y but also by the primary transfer power supplies 81M, 81C and 81Bk for M, C and Bk. Then, in the primary transfer nips for M, C, and Bk, the potential difference between the background portion of the photoconductor and the intermediate transfer belt becomes larger than the discharge start voltage, so the toner on the belt is used as the background of the photoconductor. It will be reverse transferred to the part.

As described above, reverse transfer of the toner image is likely to occur in the primary transfer nip for M, C, and Bk. On the other hand, reverse transfer of the toner image does not occur in the primary transfer nip for Y. Therefore, with respect to the primary transfer power supply 81Y for Y, the target value of the primary transfer current is made smaller as the image area ratio of the section at the transfer nip exit becomes higher within the voltage range where the primary transfer efficiency does not decrease. Yes. Specifically, based on the image area ratio x1 (0 ≦ x1 ≦ 1) of the section in the vicinity of the nip exit of the photoreceptor 2Y, the target value I _1Y (x1) of the primary transfer current for the primary transfer power supply 81Y for Y is calculated. The control unit 200 is configured so as to be obtained based on the following equation (1).
I _1Y (x1) = − 8.00 × x1 + 28.0 [μA] (1)

  With reference to FIGS. 10 and 11, the above formula (1) sets the primary transfer voltage in the vicinity of 1900 [V] regardless of the image area ratio in the vicinity of the nip exit of the photoconductor, and the high transfer efficiency of Y toner. It is determined as a linear function that can obtain the target value to be realized. Thus, by changing the primary transfer current according to the image area ratio x1, a sufficient amount of primary transfer current is generated between the image portion of the photoreceptor 2Y and the intermediate transfer belt 21 in the primary transfer nip for Y. It is possible to achieve good primary transfer efficiency.

The above is a description of the Y-color process unit, but high-quality images can be obtained by performing similar control for the M, C, and Bk process units. Specifically, for the M color process unit, the primary transfer current of the primary transfer power source 81M for M is determined based on the image area ratio x2 (0 ≦ x2 ≦ 1) of the section near the nip exit of the photoreceptor 2M. The control unit 200 is configured to obtain the target value I _1M (x2) based on the following equation (2). For the C color process unit, the primary transfer current target value I for the C primary transfer power supply 81C is based on the image area ratio x3 (0 ≦ x3 ≦ 1) of the section in the vicinity of the nip exit of the photoreceptor 2C. _The control unit 200 is configured to obtain _1C (x3) based on the following equation (3). The reason why the currents M and C applied to the image area ratio are relatively smaller than in the case of the Y color process unit is to reduce reverse transfer.
I _1M (x2) = − 7.9 × x2 + 26.4 [μA] (2)
I _1C (x3) = − 7.4 × x3 + 24.4 [μA] (3)

On the other hand, for the primary transfer current target value I _1Bk (x4) of the primary transfer power source 81Bk for Bk, the calculation formulas used for primary transfer of the image toner image and primary transfer of the sticking toner image are different. ing. Specifically, when the image area (the area on the photoconductor where the toner image for image exists and the toner image for pasting does not exist) exists in the primary transfer nip, the area near the nip exit of the photoconductor 2Bk. Based on the image area ratio x4 (0 ≦ x4 ≦ 1) of the section, the primary transfer current target value I _1Bk (x4) for the primary transfer power supply 81Bk for Bk is obtained based on the following equation (4): The control unit 200 is configured. Further, when the binding margin area (the area on the photoconductor where the toner image for pasting exists) exists in the primary transfer nip, the image area ratio x4 (0 ≦ x4 ≦ 1) of the section near the nip exit of the photoconductor 2Bk. ), The control unit 200 is configured to obtain the primary transfer current target value I ₁ ′ _Bk (x4) of the primary transfer power supply 81Bk for Bk based on the following equation (5).
I _1Bk (x4) = − 7.4 × x4 + 24.4 [μA] (4)
I ₁ ′ _Bk (x4) = − 4.9 × x4 + 24.4 [μA] (5)

  In this embodiment, the toner adhesion amount per unit area of the stuck toner image is about 1.5 times that of the solid image for image. According to the present embodiment, the value of the primary transfer current flowing through the primary transfer nip is larger than that of the solid image for image even when the sticking toner image has the same image area ratio as the solid image for image. Therefore, since the amount of the primary transfer current flowing through the sticking toner image is larger than the amount of the primary transfer current flowing through the solid image for image, a high transfer rate can be realized for the sticking toner image.

  As for the primary transfer current that flows when the image area is present in the primary transfer nip, the same value as the primary transfer current that flows when the binding area is present in the primary transfer nip is used in this way. There is no need to switch the transfer current control between the image area and the binding area. However, if the same value as the primary transfer current that flows when the binding area is present in the primary transfer nip is used as the primary transfer current that flows when the image area exists in the primary transfer nip, the toner image for image The primary transfer current flowing through the head becomes excessive, causing problems such as a reduction in the transfer rate of the image toner image. Therefore, it is important to vary the amount of primary transfer current that flows between the image area and the binding area.

Further, in the present embodiment, the secondary transfer current flowing through the sticking toner image T during the secondary transfer is larger than the secondary transfer current flowing through the solid image for image during the secondary transfer of the solid image for image. Thus, the secondary transfer bias applied to the secondary transfer roller 26 is also controlled. Contrary to the case of the primary transfer current, the secondary transfer current that flows to the image toner image is controlled such that the higher the image area ratio, the larger the current that flows. Specifically, the secondary transfer current target values I _1Y (x1), I _1M (x2), I _1C (x3), and I _1Bk (x4) of the secondary transfer current are set according to the image area ratios x1 to x4 of the respective colors. calculated, and the sum of their color target value to calculate a target value I ₂ of the secondary transfer current.

The target values I _1Y (x1), I _1M (x2), and I _1C (x3) of the secondary transfer currents for M, C, and Bk are obtained based on the following equations (6) to (8), respectively. Note that the amount of secondary transfer current with respect to the image area ratio is relatively large in the order of C, M, and Y because the process unit disposed on the upstream side in the endless movement direction of the intermediate transfer belt 21 is downstream of the process unit. This is because the amount of charge increases in response to the primary transfer current during the primary transfer of the process unit arranged on the side, and the amount of secondary transfer current required to obtain a high secondary transfer rate increases.
I _2Y (x1) = − 10.5 × x1 −15 [μA] (6)
I _2M (x2) = − 9.4 × x2 −15 [μA] (7)
I _2C (x3) = − 7.4 × x3 −15 [μA] (8)

On the other hand, with respect to the target value I _2Bk (x4) for each color of the secondary transfer current for Bk, the calculation formulas used for the secondary transfer of the image toner image and the secondary transfer of the sticking toner image are different. ing. Specifically, the color-specific target value I _2Bk (x4) of the secondary transfer current of the image toner image is obtained based on the following equation (9), and the color-specific target value of the secondary transfer current of the stuck toner image: I ₂ ′ _Bk (x4) is obtained based on the following equation (1-).
I _2Bk (x4) = − 4.2 × x4 −15 [μA] (9)
I ₂ ′ _Bk (x4) = − 6.3 × x4 −15 [μA] (10)

  According to the present embodiment, the value of the secondary transfer current flowing through the secondary transfer nip is larger than that of the solid image for image even when the toner image to be stuck has the same image area ratio as that of the solid image for image. Therefore, since the amount of the secondary transfer current flowing through the sticking toner image is larger than the amount of the secondary transfer current flowing through the solid image for image, a high transfer rate can also be realized for the sticking toner image.

Next, an experimental result of evaluating the magnitude of the sticking force when the belt-like sticking toner image T shown in FIG. 4 is formed on the binding portion A of the paper P will be described. In this experiment, evaluation was made in four stages (（, ○, Δ, ×) based on the difficulty of peeling. The evaluation results are as shown in Table 1 below.

In Comparative Example 1, the toner adhesion amount (M / A) per unit area of the toner image T to be stuck on the photoreceptor is 0.45 [mg / cm ² ], which is the same as that of the solid toner image, and the primary transfer current and The target value of the secondary transfer current is the same value as that of the image toner image. The evaluation of the sticking power in this case was the lowest rank “×”.
In Comparative Example 2, the toner adhesion amount (M / A) per unit area of the toner image T to be stuck on the photoreceptor is 0.65 [mg / cm ² ], which is larger than that of the solid toner image, but primary transfer is performed. The same values as those for the image toner image are used as target values for the current and the secondary transfer current. The evaluation of the sticking power in this case was the second “Δ” from the lowest rank.

In Example 1, the toner adhesion amount (M / A) per unit area of the toner image T to be stuck on the photoconductor is 0.65 [mg / cm ² ], which is larger than that of the solid toner image, and the primary transfer current. As the target value of the secondary transfer current, a value larger than that of the image toner image is used. The evaluation of the sticking power in this case was the highest rank “◎”.
In Example 2, the toner adhesion amount (M / A) per unit area of the toner image T to be stuck on the photoreceptor is 0.65 [mg / cm ² ], which is larger than that of the solid toner image, and the primary transfer current. As the target value, a value larger than that of the image toner image was used. However, as the target value of the secondary transfer current, the same value as that of the image toner image was used. The evaluation of the sticking power in this case was “○”, which was the second highest from the highest rank, although it did not reach the highest rank.
In Example 3, the toner adhesion amount (M / A) per unit area of the toner image T to be stuck on the photoreceptor is 0.65 [mg / cm ² ], which is larger than that of the solid toner image, and the primary transfer current. The same value as that of the image toner image was used as the target value of the image, but the value larger than that of the image toner image was used as the target value of the secondary transfer current. The evaluation of the sticking power in this case was “○”, which was the second highest from the highest rank, although it did not reach the highest rank.

  By the way, in this embodiment, since the transfer current that flows when the sticking toner image passes through the transfer nip is controlled according to the image area ratio, the image area ratio of the sticking toner image is particularly variable. It has a great effect on the configuration. For example, when the long belt-like sticking toner image shown in FIG. 4 and two short belt-like sticking toner images as shown in FIG. 13 can be selected, in this embodiment, each image area ratio Since an optimum transfer current can be applied according to the difference, a high transfer rate can be obtained for any sticking toner image. Therefore, even if any sticking toner image is selected, a corresponding strong sticking force can be obtained.

  In a configuration in which the image area ratio of the sticking toner image is constant, a predetermined fixed value may be used for the transfer current that flows through the sticking toner image. In the configuration in which the transfer current value is also a fixed value for the image toner image (the configuration in which the transfer current value is not changed in accordance with the image area ratio), at least the secondary transfer current that flows through the toner image to be attached is A transfer current larger than that of the solid toner image is applied to the toner image to be stuck.

  In this embodiment, a method of controlling the developing bias is employed as a method for increasing the toner adhesion amount per unit area of the toner image to be stuck on the photoconductor than the solid toner image, but this is not limited thereto. I can't. For example, a method of controlling the exposed portion potential of the photosensitive member or controlling a linear velocity difference between the photosensitive member and the developing sleeve may be used. When the developing method is a one-component developing method, depending on the configuration, the developer supply member that changes the pressing force of the regulating blade (developer regulating member) against the developing roller or supplies the developer to the developer carrying member The potential difference between the developing roller and the developer carrying member and the potential difference between the developing roller and the regulating blade may be controlled.

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 of the intermediate transfer belt 21 or the like is formed by using a toner image forming unit such as the Bk process unit 1Bk and a toner image for image based on the image information and a toner image for attaching a binding portion of a sheet of paper P or the like. The transfer bias is applied to a transfer region such as a secondary transfer nip formed between the image carrier and the sheet by a transfer means such as a secondary transfer roller 26 or a secondary transfer power source 82. An image toner image is transferred from the image carrier onto a sheet to form an image on the sheet, and the transfer toner is applied to the transfer region by the transfer means to thereby apply the image to be stuck to the image. In the image forming system for transferring from the body onto the binding portion A of the sheet and sticking the binding portion between the sheets by the sticking force of the sticking toner image, the toner image forming means includes the image toner image The Forming the sticking toner image on the image carrier with a toner sticking amount larger than the maximum toner sticking amount per unit area when forming, and the transfer means transfers the sticking toner image to the binding margin of the sheet When the transfer current flowing through the toner image to be transferred is transferred onto the sheet, the image toner image having the maximum toner adhesion amount per unit area (solid image for image) is transferred to the sheet. The transfer bias is applied so as to be larger than the flowing transfer current.
According to this, the toner image forming unit forms a sticking toner image having a toner adhesion amount larger than the maximum toner adhesion amount per unit area when the image toner image is formed on the image carrier. At this time, the transfer current amount that flows through the sticking toner image during transfer to the sheet is the same as the transfer current that flows through the image toner image when transferring the image toner image having the maximum toner adhesion amount per unit area to the sheet, or If it is smaller than this, the transfer current is insufficient to transfer the stuck toner image onto the sheet at a sufficient transfer rate. That is, the toner image to be attached is close to the transfer rate of the image toner image unless the transfer current is increased by an amount corresponding to the amount of toner adhesion per unit area larger than that of the image toner image having the maximum toner adhesion amount. An equivalent transfer rate cannot be obtained. In this case, even if a sticking toner image having a toner adhesion amount larger than the maximum toner adhesion amount per unit area of the image toner image is formed on the image carrier, the sticking toner that adheres to the binding portion of the sheet The toner adhesion amount per unit area of the image cannot be increased sufficiently. According to this aspect, the transfer current that flows through the stuck toner image during transfer onto the sheet is used to transfer the image toner image with the maximum toner adhesion amount (so-called solid image toner image) onto the sheet. The transfer current flowing through the toner image is larger. As a result, the toner image to be stuck on the image carrier having a larger toner adhesion amount per unit area than the image toner image having the maximum toner adhesion amount can be transferred at a transfer rate close to or equivalent to the transfer rate of the image toner image. , And can be transferred to the binding portion of the sheet. Therefore, it is possible to sufficiently increase the toner adhesion amount per unit area of the toner image to be adhered that adheres to the binding portion of the sheet.

(Aspect B)
An image toner image based on the image information and a toner image to be attached for adhering a binding portion of a sheet such as paper P are formed by toner image forming means such as a charging device, an optical writing unit 90, and a developing device 3Bk. A transfer bias is formed on an image carrier such as the photosensitive member 2Bk and transferred to a transfer region between the image carrier and an intermediate transfer member such as the intermediate transfer belt 21 by a transfer means such as a primary transfer roller 25Bk and a primary transfer power source 81Bk. The image toner image is transferred from the image carrier onto the intermediate transfer member by applying the toner image, and then transferred from the intermediate transfer member onto the sheet to form an image on the sheet. By applying a transfer bias to the transfer region, the sticking toner image is transferred from the image carrier to the intermediate transfer member, and then transferred from the intermediate transfer member onto the binding area A of the sheet. of In the image forming system in which the binding portion between the sheets is adhered by the adhesion force, the toner image forming unit has a toner adhesion amount larger than a maximum toner adhesion amount per unit area when forming the image toner image. The sticking toner image is formed on an image carrier, and the transfer unit transfers a sticking toner image onto the intermediate transfer member, and a transfer current flowing through the sticking toner image is per unit area. The transfer bias is applied so as to be larger than a transfer current flowing through the image toner image when the image toner image having the maximum toner adhesion amount is transferred onto the intermediate transfer member.
Also in this embodiment, as in the above-described embodiment A, the toner image to be stuck on the image carrier having a larger toner adhesion amount per unit area than the image toner image (solid image image) that is the maximum toner adhesion amount The toner image can be transferred to the binding portion of the sheet at a transfer rate close to or equivalent to the transfer rate of the toner image. Therefore, it is possible to sufficiently increase the toner adhesion amount per unit area of the toner image to be adhered that adheres to the binding portion of the sheet.

(Aspect C)
In the aspect A or B, the toner image forming unit forms the sticking toner image on the upstream side or the downstream side in the image carrier surface movement direction with respect to the image toner image, and the transfer unit includes the sticking image. The transfer bias applied to the transfer region is switched between when the worn toner image is present in the transfer region and when the image toner image is present in the transfer region.
According to this, it is possible to easily realize a configuration in which different transfer currents are supplied to the image toner image and the sticking toner image.

(Aspect D)
In any one of the aspects A to C, the transfer unit controls the transfer bias so that the amount of transfer current flowing through the transfer region changes according to the area ratio of the toner image existing in the transfer region. A transfer current amount flowing through the transfer region when the toner image including the sticking toner image is present in the transfer region at a predetermined toner image area ratio does not include the sticking toner image; The transfer bias is set so that a toner image including the image toner image has a toner image area ratio equal to the predetermined toner image area ratio and is larger than a transfer current flowing in the transfer area when the toner image is present in the transfer area. It is characterized by controlling.
According to this, in the configuration in which the area of the sticking toner image can be changed, it becomes possible to flow an optimum transfer current according to the difference in the respective image area ratios, and a high transfer rate is obtained for any sticking toner image. can get. Therefore, even if any sticking toner image is selected, a corresponding strong sticking force can be obtained.

(Aspect E)
In any one of the aspects A to D, the toner image forming unit changes an area of the sticking toner image formed on the image carrier in accordance with a predetermined condition.
According to this, since the area of the sticking toner image can be changed, the sheet can be stuck in a plurality of sticking modes.

DESCRIPTION OF SYMBOLS 1 Process unit 2 Photoconductor 3 Developing device 4 Charging device 21 Intermediate transfer belt 25 Primary transfer roller 26 Secondary transfer roller 40 Fixing device 50 Paper post-processing device 51 Entrance 52 Switching claw 53 Processing conveyance path 54 Conveying belt 55 Linear conveyance Path 56 Conveying roller 58 Paper discharge unit 60 Binding processing unit 61 Stacking unit 62 Receiving unit 63 Pressure unit 64, 65 Heat sink 72, 73 Heater 81 Primary transfer power source 82 Secondary transfer power source 90 Optical writing unit 100 Printer 200 Control unit

JP-A-49-1333039 Japanese Utility Model Publication No. 3-50470

Claims (6)

An image toner image based on image information and a sticking toner image for sticking a binding portion of a sheet are formed on an image carrier by a toner image forming unit, and the image carrier and sheet are placed between the image carrier and the sheet. By applying a transfer bias to the transfer area by a transfer means, the image toner image is transferred from the image carrier onto the sheet to form an image on the sheet, and the transfer means transfers the transfer bias to the transfer area. In the image forming system in which the sticking toner image is transferred from the image carrier onto the binding portion of the sheet by applying the toner, and the binding portion between the sheets is attached by the sticking force of the sticking toner image ,
The toner image forming means uses an image forming condition that is different from the image forming condition for forming the image toner image, so that the maximum toner adhesion amount per unit area when the image toner image is formed. Forming the sticking toner image once on the image carrier with a large amount of toner adhesion,
When the transfer means transfers the sticking toner image onto the binding portion of the sheet, the transfer current flowing through the sticking toner image causes the image toner image having the maximum toner adhesion amount per unit area onto the sheet. An image forming system, wherein the transfer bias is applied so as to be larger than a transfer current flowing through the image toner image during transfer. An image toner image based on image information and a sticking toner image for sticking the binding portion of the sheet are formed on the image carrier by toner image forming means, and the image carrier and the intermediate transfer member The image toner image is transferred from the image carrier onto the intermediate transfer member by applying a transfer bias to the intermediate transfer region by transfer means, and then transferred onto the sheet from the intermediate transfer member. The transfer toner image is transferred from the image carrier to the intermediate transfer member by applying a transfer bias to the transfer region by the transfer means, and then transferred from the intermediate transfer member onto the binding margin of the sheet. In an image forming system for transferring to and sticking the binding portion between sheets by the sticking force of the sticking toner image,
The toner image forming means uses an image forming condition that is different from the image forming condition for forming the image toner image, so that the maximum toner adhesion amount per unit area when the image toner image is formed. Forming the sticking toner image once on the image carrier with a large amount of toner adhesion,
When the transfer means transfers the sticking toner image onto the intermediate transfer body, the transfer current that flows through the sticking toner image displays an image toner image having a maximum toner adhesion amount per unit area. An image forming system, wherein the transfer bias is applied so as to be larger than a transfer current flowing through the image toner image when transferred upward.   The image forming system according to claim 1 or 2,
  The image forming system according to claim 1, wherein the image forming condition is a developing voltage when the image toner image or the sticking toner image is developed.   The image forming system according to any one of claims 1 to 3,
  The image forming system, wherein the toner image to be stuck is formed with one kind of toner. The image forming system according to any one of claims 1 to 4 ,
The toner image forming unit forms the sticking toner image on the upstream side or the downstream side in the image carrier surface movement direction with respect to the image toner image;
The transfer means switches the transfer bias applied to the transfer area between when the sticking toner image exists in the transfer area and when the image toner image exists in the transfer area. A featured image forming system. The image forming system according to any one of claims 1 to 5 ,
The transfer means controls a transfer bias so that a transfer current amount flowing through the transfer region changes according to an area ratio of the toner image existing in the transfer region, and includes the sticking toner image. When a toner image is present in the transfer region at a predetermined toner image area ratio, the amount of transfer current flowing through the transfer region is such that the toner image including the image toner image does not include the sticking toner image. An image forming system, wherein a transfer bias is controlled to be larger than an amount of transfer current flowing through the transfer region when the toner image area rate is the same as the toner image area rate.

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