JP2020038389A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that has suppressed the occurrence of image defects due to a wax aggregate that is likely to be generated at an edge part of a cleaning blade.SOLUTION: When performing image formation on a second surface (rear face) of a recording material P (YES in S3), a control part executes toner band forming control of forming a toner band on a secondary transfer belt (S4). In this case, the control part controls an image forming apparatus to form the toner band on the secondary transfer belt in a space between a recording material and a recording material. The toner band is formed, of areas corresponding to spaces between the continuous recording materials, at least in any one of areas before and after the second surface. The formed toner band is conveyed to a cleaning blade. This configuration prevents a wax scraped off from the secondary transfer belt by the cleaning blade from remaining held between an edge part and the secondary transfer belt. In other words, this configuration prevents the generation of a wax aggregate and suppress the occurrence of image defects due to the wax aggregate.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image forming apparatus that forms a toner image on a recording material using an electrophotographic method or the like.

  Conventionally, a toner image formed on a photosensitive drum is primarily transferred to an intermediate transfer member, and a toner image primarily transferred to the intermediate transfer member is secondarily transferred to a recording material at a transfer nip formed between the image and the secondary transfer member. 2. Description of the Related Art An intermediate transfer type image forming apparatus that performs transfer is known. Further, in a recent image forming apparatus, a toner containing wax is used in order to easily separate a recording material from a fixing device in order to cope with high speed. When an image is formed on both sides of a recording material using this toner, the recording material after the completion of image formation on the first surface (front surface) is heated to fix the toner and has heat. The recording material has oozed out. When the image is formed on the second side (back side) of the recording material from which the wax has leached and the surface is reversed, the wax may transfer from the first side (front side) of the recording material to the secondary transfer body and adhere thereto.

  Wax attached to the secondary transfer member may cause image defects such as causing image unevenness during image formation and reducing image density. Therefore, in order to remove the wax attached to the secondary transfer body, an image forming apparatus that heats the secondary transfer body, melts the wax attached to the secondary transfer body, and collects the melted wax by wax collection means has been proposed. It has been proposed (Patent Document 1). Further, an image forming apparatus has been proposed in which a lubricant is applied to the surface of a secondary transfer body to remove wax by a cleaning member and a cleaning auxiliary member, thereby suppressing adhesion of the wax to the secondary transfer body ( Patent Document 2).

JP 2013-7796A JP 2012-2904 A

  However, the apparatus described in Patent Document 1 includes a heating unit and a wax recovery unit for heating the secondary transfer body, and the apparatus described in Patent Document 2 includes a mechanism for applying a lubricant and a cleaning auxiliary unit. Are likely to be complicated and costly. Then, the wax scraped off from the secondary transfer member by the cleaning blade accumulates and accumulates between the edge portion of the cleaning blade and the secondary transfer member, and a wax lump is easily generated. When the wax mass occurs, a cleaning failure occurs in which the toner passes through the cleaning blade, and as a result, for example, a streak-like image defect is likely to occur on the recording material.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has as its object to provide an image forming apparatus capable of suppressing the occurrence of an image defect due to a lump of wax that easily occurs at an edge portion of a cleaning blade.

  An image forming apparatus according to an aspect of the invention includes an image forming unit configured to develop a toner image on the image carrier using a toner including wax, and an image forming unit configured to contact the image carrier with the image carrier. A transfer rotator that forms a transfer portion in the transfer portion and transfers a toner image from the image bearing member to a recording material in the transfer portion; and a rotator that transports the toner removed from the transfer rotator or the transfer rotator. , A blade capable of removing toner on the transfer rotating body or the rotating body, a fixing device for heating and fixing a toner image formed on the recording material, and a recording material passing through the fixing device A transport unit that reverses the front and back and transports to the transfer unit, and in a double-sided printing mode in which toner images are formed on both surfaces of a plurality of recording materials, the second recording material following the preceding first recording material, Transfer at transfer section Based on the information as to whether the surface to be printed is the second surface, in a region corresponding to between the first recording material and the second recording material, so as to form a supply toner image for supplying to the blade. And a control unit for controlling the image forming unit.

  ADVANTAGE OF THE INVENTION According to this invention, since the wax scraped off by the blade is hard to accumulate at the edge portion to form a wax lump, it is possible to particularly suppress the occurrence of image defects due to the wax lump.

FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus according to a first embodiment. 5 is a flowchart illustrating an image forming process according to the first embodiment. FIG. 4 is a diagram illustrating a toner band formed in the first embodiment. 4 is a graph illustrating a particle size distribution of a toner. 9 is a flowchart illustrating an image forming process according to the second embodiment. FIG. 9 is a diagram illustrating a toner band formed in the case of the second embodiment. 9 is a flowchart illustrating an image forming process according to a third embodiment. FIG. 13 is a diagram illustrating a toner band formed in the case of the third embodiment. 9 is a flowchart illustrating an image forming process according to a fourth embodiment. 5 is a graph showing a relationship between a toner band length and a time change of a toner amount in an edge portion. 15 is a flowchart illustrating an image forming process according to a fifth embodiment. 6 is a graph showing whether or not an image defect occurs on recording materials having different sizes for each toner band length. 13 is a flowchart illustrating an image forming process according to a sixth embodiment. 9 is a graph showing a relationship between a toner application amount and a time change of a toner amount in an edge portion. 7 is a graph showing whether or not an image defect occurs on recording materials having different sizes for each amount of applied toner. 17 is a flowchart illustrating an image forming process according to a seventh embodiment. 18 is a flowchart illustrating an image forming process according to the eighth embodiment. FIG. 4 is a diagram illustrating an image ratio of each area. 15 is a flowchart illustrating an image forming process according to a ninth embodiment. FIG. 21 is a diagram illustrating a toner band formed in the case of the ninth embodiment. FIG. 1 is a schematic diagram illustrating an image forming apparatus having an electrostatic secondary transfer belt cleaning device. FIG. 3 is a schematic diagram illustrating an electrostatic intermediate transfer belt cleaning device.

[First Embodiment]
1st Embodiment is described using FIG. 1 thru | or FIG. First, an image forming apparatus according to a first embodiment will be described with reference to FIG.

<Image forming apparatus>
The image forming apparatus 100 shown in FIG. 1 is a tandem-type intermediate transfer type multicolor printer provided with a plurality of image forming units PY, PM, PC, and PK of yellow, magenta, cyan, and black along an intermediate transfer belt 40. is there.

  In the image forming section PY, a yellow toner image is formed on the photosensitive drum 1Y and is primarily transferred to the intermediate transfer belt 40. In the image forming section PM, a magenta toner image is formed on the photosensitive drum 1M and is transferred so as to overlap the yellow toner image on the intermediate transfer belt 40. In the image forming units PC and PK, a cyan toner image and a black toner image are formed on the photosensitive drums 1C and 1K, respectively, and sequentially transferred onto the intermediate transfer belt 40. The intermediate transfer belt 40 rotates while carrying the toner image.

  The recording material P (paper, sheet material such as an OHP sheet, etc.) is taken out of the recording material cassette 31 by the pickup roller 32 and sent out to the registration roller 13. The registration roller 13 sends out the recording material P to the secondary transfer portion T2 in synchronization with the toner image on the intermediate transfer belt 40. The recording material P on which the four-color toner images have been secondarily transferred is sent to the fixing device 60, and is heated and pressed by a heating roller 60a and a pressure roller 60b as heating means. Thereby, the toner image on the recording material is heated and fixed on the recording material P.

<Image forming unit>
The image forming units PY, PM, PC, and PK have substantially the same configuration except that the colors of the toner used in the developing devices 5Y, 5M, 5C, and 5K are different from yellow, magenta, cyan, and black. Therefore, hereinafter, the image forming unit PY will be described in detail, and the image forming units PM, PC, and PK will be described by replacing Y at the end of the symbol with M, C, and K.

  In the image forming section PY, a charging device 3Y, an exposure device 4Y, a developing device 5Y, a primary transfer roller 6Y, and a drum cleaning device 7Y are arranged so as to surround the photosensitive drum 1Y. The photosensitive drum 1Y as an image carrier is a drum-shaped electrophotographic photosensitive member rotatably supported by the apparatus main body, and is rotated counterclockwise in FIG. 1 at a predetermined process speed by a photosensitive drum drive motor (not shown) (see FIG. 1). It rotates in the direction of arrow A in the figure.

  The charging device 3Y charges the surface of the photosensitive drum 1Y to a uniform negative dark potential by applying an oscillating voltage obtained by superimposing an AC voltage on a negative DC voltage. The exposure device 4Y scans, using a rotating mirror, a laser beam obtained by ON-OFF-modulating the scanning line image data obtained by developing the separated color image of each color, and writes an electrostatic latent image of the image on the charged surface of the photosensitive drum 1Y.

  The developing device 5Y supplies the negatively charged toner to the photosensitive drum 1Y to develop the electrostatic latent image into a toner image. The developing device 5Y rotates a developing sleeve (not shown) disposed on the surface of the photosensitive drum 1Y with a slight gap in a counter direction of the photosensitive drum 1Y. The developing device 5Y charges a two-component developer containing a toner and a carrier, carries the charged toner on a developing sleeve, and transports the developer to a portion facing the photosensitive drum 1Y. When an oscillating voltage obtained by superimposing an AC voltage on a DC voltage is applied to the developing sleeve, the negatively charged toner moves to the exposed portion of the photosensitive drum 1Y, which has become relatively positive, and the electrostatic image is inverted. Developed. The developer replenishing section 51Y replenishes the replenishing developer to the developing device 5Y in accordance with toner consumption accompanying image formation.

  The primary transfer roller 6Y presses the intermediate transfer belt 40 to form a primary transfer portion T1 between the photosensitive drum 1Y and the intermediate transfer belt 40. A primary transfer high voltage power supply D1 is connected to the primary transfer roller 6Y, and the primary transfer high voltage power supply D1 applies a positive primary transfer bias voltage to the primary transfer roller 6Y, so that the photosensitive drum 1Y is negatively charged. The toner image is transferred to the intermediate transfer belt 40. In FIG. 1, the primary transfer high-voltage power supply D1 is connected only to the primary transfer roller 6Y for convenience of illustration, but the primary transfer high-voltage power supply is also connected to the other primary transfer rollers 6M, 6C, and 6K. Of course.

  The drum cleaning device 7Y is in contact with the photosensitive drum 1Y, and removes toner, paper dust, and the like that have passed through the primary transfer portion T1 and adhered to the photosensitive drum 1Y from the photosensitive drum 1Y.

<Intermediate transfer belt>
The intermediate transfer belt 40 is an intermediate transfer member that can rotate while being in contact with the photosensitive drum 1Y. The intermediate transfer belt 40 is supported by being stretched over a tension roller 41, a secondary transfer inner roller 42, and a driving roller 43. The intermediate transfer belt 40 is driven by the driving roller 43 and rotates at a rotational speed of, for example, 250 to 300 mm / sec in the direction of arrow G in FIG. Rotate. The tension roller 41 stretches the intermediate transfer belt 40 at a constant tension.

The intermediate transfer belt 40 is an endless belt in which a resin layer, an elastic layer, and a surface layer are sequentially laminated on a core metal as a base from the core metal side. The resin layer is made of a resin material such as polyimide or polycarbonate, and has a thickness of 70 to 100 μm. The elastic layer is made of an elastic material such as urethane rubber and chloroprene rubber and has a thickness of 120 to 180 μm. The surface layer is required to have a small toner adhesion in order to easily transfer the toner from the intermediate transfer belt 40 to the recording material P in the secondary transfer portion T2. Therefore, for the surface layer, for example, one kind of a resin material such as polyurethane, polyester, and epoxy resin, or two or more kinds of elastic materials such as elastic rubber, elastomer, and butyl rubber are used. Further, in order to reduce the surface energy and enhance the lubricity, one or two or more kinds of powders or particles such as a fluororesin, or powders or particles having different particle diameters are dispersed in the surface layer. . The surface layer has a thickness of 5 to 10 μm. The volume resistivity of the intermediate transfer belt 40 is adjusted to, for example, 10 ⁹ Ω · cm.

  The four color toner images transferred to the intermediate transfer belt 40 are conveyed to the secondary transfer portion T2 and are collectively and secondarily transferred to the recording material P. The intermediate transfer belt cleaning device 45 is a cleaning blade that is in contact with the intermediate transfer belt 40 and is capable of removing residual toner and the like remaining on the intermediate transfer belt 40 from the intermediate transfer belt (on the intermediate transfer body) after the secondary transfer. is there. The intermediate transfer belt cleaning device 45 is, for example, a cleaning blade capable of removing toner and the like from the intermediate transfer belt 40 by being brought into contact with the rotation direction of the intermediate transfer belt 40 in the counter direction (the direction of arrow G in the drawing).

<Secondary transfer belt unit>
The secondary transfer belt unit 56 causes the recording material P to be carried on the secondary transfer belt 12 as a secondary transfer rotator and passes through the secondary transfer portion T2. The use of the secondary transfer belt 12 facilitates separation of the recording material P from the intermediate transfer belt 40 after the secondary transfer of the toner image in the secondary transfer portion T2.

  The secondary transfer belt unit 56 includes the secondary transfer belt 12, the secondary transfer outer roller 10, the separation roller 21, the tension roller 22, and the drive roller 23. The secondary transfer belt 12 contacts the intermediate transfer belt 40 to form a secondary transfer portion T2. When a transfer electric field is generated in the secondary transfer portion T2, the toner image carried on the intermediate transfer belt 40 is transferred to the recording material P. In the present embodiment, a belt-shaped supply toner image (hereinafter, referred to as a toner band) carried on the intermediate transfer belt 40 is transferred to the secondary transfer belt 12.

  The secondary transfer belt 12 is formed in an endless belt shape using a high-resistance resin material, and is stretched by a secondary transfer outer roller 10, a separation roller 21, a tension roller 22, and a drive roller 23. The secondary transfer belt 12 rotates in the direction of arrow B in the figure at, for example, 300 mm / sec in synchronization with the intermediate transfer belt 40, and passes the recording material P sent out by the registration roller 13 through the secondary transfer portion T2 to fix the recording material P. Conveyed to 60. The secondary transfer belt 12 is charged when the toner image carried on the intermediate transfer belt 40 is transferred onto the recording material P, and is conveyed in close contact with the recording material P, while the recording material P on which the toner image has been transferred is conveyed. It is separated from the intermediate transfer belt 40 and sent to the fixing device 60 side.

The secondary transfer belt 12 is an endless belt formed using a resin material such as polyimide or polycarbonate containing an appropriate amount of carbon black as an antistatic agent. The volume resistivity of the secondary transfer belt 12 is adjusted to 10 ⁹ to 10 ¹⁴ Ω · cm. The secondary transfer belt 12 has a thickness of 0.07 to 0.1 mm. Further, the secondary transfer belt 12 has a Young's modulus of 100 MPa or more and less than 10 GPa as measured by a tensile test method (JIS K6301).

  The outer secondary transfer roller 10 is pressed into contact with the inner secondary transfer roller 42 via the intermediate transfer belt 40 and the secondary transfer belt 12, and a secondary transfer portion is provided between the intermediate transfer belt 40 and the secondary transfer belt 12. Form T2. The secondary transfer outer roller 10 is provided with a secondary transfer high-voltage power supply 11 having a variable bias voltage. The bias voltage of the secondary transfer high-voltage power supply 11 is controlled at a constant current so that a transfer current of +40 to 60 μA flows. While the secondary transfer inner roller 42 is connected to the ground potential (0 V), a positive bias voltage (secondary transfer voltage) having a polarity opposite to that of the toner is applied to the secondary transfer outer roller 10 by the secondary transfer high voltage power supply 11. As a result, a transfer electric field is generated in the secondary transfer portion T2. In response to the transfer electric field, the yellow, magenta, cyan, and black negative toner images carried on the intermediate transfer belt 40 are collectively and secondarily transferred to the recording material P. In the present embodiment, the toner band is secondarily transferred from the intermediate transfer belt 40 to the secondary transfer belt 12.

The outer secondary transfer roller 10 is formed by laminating an elastic layer of ion conductive foamed rubber (NBR rubber) on a core metal as a base. The outer secondary transfer roller 10 is formed, for example, to have an outer diameter of 24 mm. The elastic layer has a surface roughness Rz of 6.0 to 12.0 μm and an Asker-C hardness of about 30 to 40. The elastic layer has an electric resistance value of 10 ⁵ to 10 measured when a voltage of 2 kV is applied under a normal temperature and normal humidity environment (N / N environment: temperature 23 ° C., humidity 50% RH). ⁷ Ω.

  The separation roller 21 separates the recording material P from the secondary transfer belt 12 downstream of the secondary transfer portion T2 in the rotation direction of the secondary transfer belt 12. Specifically, after the recording material P on the secondary transfer belt 12 reaches the separation roller 21, the recording material P is separated from the secondary transfer belt 12 by curvature separation on the curved surface of the secondary transfer belt 12 along the peripheral surface of the separation roller 21. I do.

  The drive roller 23 is connected to a drive motor (not shown), and drives the secondary transfer belt 12 to rotate in the direction of arrow B in the figure. The tension roller 22 has a pressure spring (not shown). By urging the secondary transfer belt 12 from the inside to the outside by the urging force of the pressure spring, a predetermined tension is applied to the secondary transfer belt 12. Has been granted.

  The recording material P having a curvature separated from the secondary transfer belt 12 is conveyed to the conveyance belt 61 and sent to the fixing device 60. The recording material on which the toner image has been fixed by the fixing device 60 is discharged out of the image forming apparatus 100. However, the recording material P on which the toner image is fixed has a first side (front surface) in a single-sided printing mode in which an image is formed on only one side of the recording material P and a double-sided printing mode in which an image is formed on both sides of the recording material P. Are different after the toner image is fixed.

  In the one-sided printing mode, the recording material P that has passed through the fixing device 60 is discharged as it is from the machine through the discharge rollers 33. On the other hand, in the double-sided printing mode, the recording material P on which the toner image has been fixed passes through the reversing conveyance path 34 and the double-sided conveyance path 35 as a conveyance section, and the second side (rear side) opposite to the first side becomes the image forming surface. That is, the sheet is re-conveyed to the secondary transfer portion T2 after being turned upside down. More specifically, the recording material P that has passed through the fixing device 60 is sent to the reverse transport path 34, and the front and rear ends are switched by performing a switchback operation in the reverse transport path 34, and then the transport is performed to the double-side transport path 35. You. The double-sided conveyance path 35 conveys the recording material P again to the secondary transfer portion T2 by joining the recording material P to the registration roller 13. In this case, the recording material P is discharged to the outside of the machine through the discharge roller 33 after the toner image is transferred to the second surface (back surface) and the toner image is fixed. The reversing conveyance path 34 and the two-sided conveyance path 35 can accommodate a plurality of recording materials P and convey them simultaneously.

  A cleaning blade 90 as a cleaning unit can contact the secondary transfer belt 12 to scrape toner and the like adhered to the secondary transfer belt 12 from the secondary transfer belt 12 (on the secondary transfer rotating body). For example, a rubber blade made of urethane rubber is used. The cleaning blade 90 is abutted in the counter direction with respect to the rotation direction of the secondary transfer belt 12 (the direction of arrow C in the figure), and scrapes toner and the like from the secondary transfer belt 12. The toner and the like scraped off from the secondary transfer belt 12 are discharged to a collection container (not shown).

<Two-component developer>
In the developing device 5Y, for example, a two-component developer containing a toner (non-magnetic) having a negative charge characteristic and a carrier having a positive charge characteristic is used as a developer. The toner is composed of colored resin particles containing a binder resin (also called a binder), a colorant, and other additives as necessary, and colored particles externally added with an external additive such as fine colloidal silica powder. Have. For example, the toner is a negatively chargeable polyester resin, and the average particle size is preferably 5 μm or more and 8 μm or less. In this embodiment, a toner having an average particle diameter of 7 μm is used.

  Further, the toner contains wax to improve the releasability from the fixing device 60 and the fixability of the toner when the toner image is fixed on the recording material P. As the wax, for example, a polyolefin wax, a long-chain hydrocarbon wax, a dialkyl ketone wax, an ester wax, an amide wax, or the like is used. The melting point of the wax is usually from 40 to 160C, preferably from 50 to 120C, and more preferably from 60 to 90C. When the melting point is within this range, the heat resistance of the toner is secured, and even when fixing is performed at a low temperature, image formation is performed without causing image defects such as cold offset. Incidentally, the content of the wax in the toner is preferably 3% by mass to 30% by mass.

As the carrier, for example, metals such as surface-oxidized iron or unoxidized iron, nickel, cobalt, manganese, chromium, and rare earths, and alloys thereof, or oxide ferrite can be preferably used. Is not particularly limited. The carrier has a volume average particle size of 20 to 50 μm, preferably 30 to 40 μm, and a volume resistivity of 10 ⁷ Ωcm or more, preferably 10 ⁸ Ωcm or more. In this embodiment, a carrier having a volume average particle size of 40 μm, a volume resistivity of 5 × 10 ⁸ Ωcm, and a magnetization amount of 260 emu / cc was used.

  The volume average particle size of the toner and the carrier was measured by the following device and method. As a measuring device, a Coulter counter TA-II type (manufactured by Coulter Inc.), an interface (manufactured by Nikkaki) for outputting a number average distribution and a volume average distribution, and a personal computer were used. In addition, a 1% NaCl aqueous solution prepared using primary sodium chloride was used as the electric field aqueous solution.

  The measuring method is as shown below. 0.1 ml of a surfactant, preferably an alkylbenzenesulfonate, is added as a dispersant to 100 to 150 ml of the electric field aqueous solution, and about 0.5 to 50 mg of a measurement sample is further added. The aqueous solution of the electric field in which the measurement sample is suspended is subjected to a dispersion treatment using an ultrasonic disperser for about 1 to 3 minutes, and the particle size distribution of 2 to 40 μm particles is measured using a 100 μm aperture as an aperture by a Coulter counter TA-II. Measure to determine the volume average distribution. From the volume average distribution thus obtained, a volume average particle size is obtained.

  The volume resistivity of the carrier was measured by the following method. Using a sandwich type cell having a measuring electrode area of 4 cm and an electrode spacing of 0.4 cm, an applied voltage E (V / cm) between both electrodes is applied to one of the electrodes under a pressure of 1 kg and applied to the circuit. It was measured by a method of obtaining the carrier resistivity from the flowing current.

  The cleaning blade 90 described above can scrape off the wax attached to the secondary transfer belt 12 in addition to the toner attached to the secondary transfer belt 12. However, since wax has tackiness unlike toner and the like, the scraped-off wax tends to accumulate and accumulate on the edge portion 90a of the cleaning blade 90, and the amount of accumulated wax increases as the number of images formed in double-sided printing increases. Increases. Then, if the height of the deposited wax (wax lump) becomes such that the toner can pass through the toner, defective cleaning of the toner occurs, and as a result, an image defect may occur on the recording material P.

  In view of the above, in the present embodiment, toner is forcibly supplied to the cleaning blade 90 during a continuous image forming job, so that the scraped wax is not deposited on the edge 90a of the cleaning blade 90.

<Control unit>
As shown in FIG. 1, the image forming apparatus 100 includes a control unit 200 and an operation unit 201. The control unit 200 is, for example, a CPU that performs various controls of the image forming apparatus 100 and has a memory such as a ROM or a RAM. Various programs and data for controlling the image forming apparatus 100 are stored in the memory. The operation unit 201 is, for example, an external terminal such as a scanner or a personal computer, or an operation panel that accepts a user's instruction to start execution of various programs such as a continuous image forming job and various data inputs. In this embodiment, the user can use the operation unit 201 to designate a double-sided print mode in which images are formed on both sides of the recording material P and a single-sided print mode in which images are formed only on one side of the recording material P. Also, a multi-color mode in which a plurality of colors (multi-color) toner images can be formed by combining several colors of yellow, magenta, cyan, and black, and a single color in which a toner image can be formed with only one desired color such as black The mode can be specified. Further, the size and the transport direction (for example, A3 portrait, A4 landscape, etc.) of the recording material P can be designated.

  When an instruction to start a continuous image forming job in any of the print modes is issued from the operation unit 201, the control unit 200 performs image forming processing stored in the memory based on the image data input from the operation unit 201. Execute (program). The control unit 200 controls the image forming apparatus 100 based on the execution of the image forming process.

  Here, the continuous image forming job is a period from the start of image formation to the completion of the image forming operation based on a print signal for continuously forming images on a plurality of recording materials. More specifically, it refers to a period from a pre-rotation (preparation operation before image formation) after receiving a print command signal (input of an image forming job) to a post-rotation (operation after image formation). , The period including the sheet interval. Note that, for example, when one job is followed by another job, these are collectively determined as one job.

  FIG. 2 shows a flowchart of the image forming process executed by the control unit 200. As shown in FIG. 2, the control unit 200 determines whether or not the double-sided printing mode is instructed (S1). If it is determined that the one-sided printing mode has been instructed (NO in S1), the control unit 200 executes image forming control for forming a toner image on the first side (front side) of the recording material P (S2). Thereafter, the control section 200 goes to the processing of S6. As described above, in the one-sided printing mode, no toner band (see FIG. 3 described later) is formed on the secondary transfer belt 12.

  When it is determined that the double-sided printing mode is instructed (YES in S2), the control unit 200 determines whether the target surface (image forming surface) on which the image forming control is performed is the second surface (back surface) of the recording material P. A determination is made (S3). When it is determined that the image forming surface is not the second surface of the recording material P (NO in S3), the control unit 200 jumps to the process of S2, and executes image forming control for forming a toner image on the first surface of the recording material P. (S2). Thus, when the image forming control is performed on the first side of the recording material P in the double-sided printing mode, no toner band is formed on the secondary transfer belt 12.

  On the other hand, when it is determined that the image forming surface is the second surface (back surface) of the recording material P (YES in S3), the control unit 200 executes toner band formation control for forming a toner band on the secondary transfer belt 12 ( S4). In this case, the control unit 200 controls the image forming apparatus 100 to control the secondary transfer belt between the preceding recording material P (first recording material) and the succeeding recording material P (second recording material). 12, a toner band is formed. As will be described in detail later, the toner band is formed in at least one of the regions before and after the second surface among the regions (paper spaces) corresponding to the continuous recording materials. The control unit 200 uses the image forming unit PY to form a yellow toner band having the highest lightness of each color, and causes the formed yellow toner band to be carried on the intermediate transfer belt 40. Then, the control section 200 controls the secondary transfer high voltage power supply 11 to transfer the toner band carried on the intermediate transfer belt 40 to the secondary transfer belt 12. Thus, a yellow toner band is formed on the secondary transfer belt 12. The toner band is a solid image. For example, the length in the direction (called the width direction) intersecting the rotation direction of the intermediate transfer belt 40 is formed to be the length in the longitudinal direction of the cleaning blade 90 abutting on the secondary transfer belt 12. You. Further, the length of the intermediate transfer belt 40 in the rotation direction (referred to as toner band length) is formed to a predetermined length such as 5 mm or 15 mm.

  FIG. 3 shows a toner band formed on the secondary transfer belt 12. In FIG. 3, the toner bands finally formed on the secondary transfer belt 12 are shown in chronological order for easy understanding. Also, for convenience of explanation, the position of the recording material P is illustrated. “1” in the drawing indicates the first surface (front surface) of the recording material P, and “2” in the drawing indicates the second surface (back surface) of the recording material P. Needless to say, the recording material P shown in the figure does not actually exist, and an area including a portion corresponding to the recording material P is secured as a sheet interval. Since the toner image has already been formed on the first side of the recording material P on the second side in the figure, the position of the second side recording material P is an area where wax may possibly adhere.

  As shown in FIG. 3, the toner band 70 is formed on the secondary transfer belt 12 between papers (non-paper passing portions) between the continuous recording materials P. However, in the first embodiment, the toner band 70 is formed on the downstream side in the rotation direction of the secondary transfer belt 12 and immediately before the recording material P on the second surface. The reason why the toner is formed immediately before the recording material P is that if the supply of the toner is too fast and it takes a long time to reach the wax, the toner supplied to the cleaning blade 90 is almost scraped off with the lapse of time, and the edge portion is formed. This is because a wax mass is likely to be generated at 90a. Therefore, it is desirable that the toner band 70 be formed as soon as possible on the recording material P so that the toner reaches the cleaning blade 90 prior to the wax.

  Returning to FIG. 2, the control unit 200 executes image formation control for forming a toner image on the second surface (back surface) of the recording material P (S5). Thereafter, the control unit 200 determines whether or not to end the continuous image forming job (S6). If it is determined that the continuous image forming job is to be ended (YES in S6), the control unit 200 ends the image forming process. When it is determined that the continuous image forming job is not to be ended (NO in S6), the control unit 200 returns to the process of S1 and repeats the processes of S1 to S6.

  The inventors of the present application conducted an experiment under the following conditions in order to confirm whether or not occurrence of image defects can be suppressed by supplying toner to the cleaning blade 90. Image formation was repeatedly performed on A4 paper with the weight ratio (T / D) of the toner and the carrier in the developer at the start of the continuous image forming job being 8% and the conditions such as the image ratio and the environment being the same. To make it easier to understand the effect of the wax, the image ratio was set to 25%. The experiment is an experiment in which a continuous image forming job is performed while supplying toner to the cleaning blade 90 in the double-sided printing mode, an experiment in which a continuous image forming job is performed without supplying toner to the cleaning blade 90 in the double-sided printing mode, and a single-sided printing mode is used. Three experiments were performed to perform a continuous image forming job. In the single-sided printing mode, when an image is formed on the same number of recording materials P as in the double-sided printing mode, the number of times that the recording material P passes through the secondary transfer unit T2 is reduced by half compared to the double-sided printing mode. Therefore, in the single-sided printing mode, an image was formed on twice as many recording materials P as in the double-sided printing mode.

  When a continuous image forming job was performed without supplying toner to the cleaning blade 90 in the double-sided printing mode, a streak-like image defect occurred on the recording material P on about 10,000 sheets. Investigating the cause, it was confirmed that at the position where the streak-like image defect occurred, the toner moved from the front side of the cleaning blade 90 to the back side (from the upstream side to the downstream side in the rotation direction of the secondary transfer belt 12). . When the edge portion 90a was enlarged and examined with a microscope, it was found that the toner slipped along the side where the wax was deposited. When the height of the wax was measured, it was about 20 μm. On the other hand, the average particle size of the toner was 7 μm. That is, the wax is deposited on the edge portion 90a to a height sufficient for the toner to pass laterally, and a wax mass is generated.

  On the other hand, when a continuous image forming job is performed while supplying toner to the cleaning blade 90 in the double-sided printing mode, no image defect occurs on the recording material P even if image formation is repeatedly performed on 20,000 recording materials P. Was. Further, when a continuous image forming job was performed in the single-sided printing mode, no image defect occurred even when image formation was repeatedly performed on 40,000 sheets of recording material P. After forming an image on 40,000 sheets of the recording material P in the single-sided printing mode, the edge portion 90a was enlarged and examined with a microscope, and no wax was deposited on the edge portion 90a. On the other hand, after the image formation on 20,000 sheets of the recording material P in the double-sided printing mode (with the toner band), the edge 90a has some wax, but the measured height is 2 μm or less. It was confirmed that the average particle diameter of the toner was sufficiently smaller than 7 μm.

  As described above, in the first embodiment, the toner band 70 is formed on the downstream side in the rotation direction of the secondary transfer belt 12 and immediately before the recording material P on the second surface. If the toner band 70 is formed immediately before the recording material P, the toner reaches the edge portion 90a before the wax reaches the edge portion 90a. The toner functions as a lubricant by being sandwiched between the edge portion 90a and the secondary transfer belt 12, and passes the wax that arrives after the toner and is scraped off by the edge portion 90a as it is. As a result, the wax does not remain between the edge portion 90a and the secondary transfer belt 12 and a wax lump is less likely to be generated, so that the occurrence of an image defect due to the wax lump can be suppressed.

[Second embodiment]
The second embodiment will be described with reference to FIGS. The second embodiment is a case where a two-component developer containing a toner having a small average particle size is used as a developer. The smaller the average particle size of the toner is, the smaller the amount of the toner protruding from the 1-dot pixel is required, and it is difficult for a user who sees the toner image formed on the recording material P to recognize the noise. Therefore, a developer containing a toner having a small average particle size is used when a higher quality toner image is to be formed on the recording material P. In the first embodiment described above, a developer containing a toner having an average particle diameter of 7 μm is used, whereas in the second embodiment, a developer containing a toner having an average particle diameter of 5 μm is used.

  FIG. 4 is a diagram illustrating the particle size distribution of the toner contained in the developer. As shown in FIG. 4, as the average particle size of the toner (toner particle size) decreases, the proportion of toner having a small particle size (the number of toners) generally increases. The smaller the particle size of the toner, the smaller the amount of the toner, but the easier it is to pass through the cleaning blade 90. Therefore, when toner having a small particle diameter is supplied to the cleaning blade 90, a small amount of toner that passes through the cleaning blade 90 can extrude the wax that is sandwiched between the edge portion 90a and the secondary transfer belt 12.

  FIG. 5 is a flowchart of the image forming process according to the second embodiment. This image forming process is executed by the control unit 200. In the image forming process shown in FIG. 5, the order of the image forming process, the toner band forming control (S4), and the image forming control (S5) shown in FIG. 2 is merely interchanged. Omitted.

  In the image forming process shown in FIG. 5, after forming a toner image on the second surface of the recording material P (S5), a toner band is formed on the secondary transfer belt 12 (S4). FIG. 6 shows a toner band formed on the secondary transfer belt 12 when the image forming process according to the second embodiment is performed.

  As shown in FIG. 6, the toner band 71 is formed between the recording materials P (non-paper passing portion) between the recording materials P. In the second embodiment, the toner band 71 is formed by the secondary transfer belt 12. Is formed immediately after the recording material P on the second surface on the upstream side in the rotation direction of. The toner band 71 uses the same image forming portion PY as in the first embodiment, and is formed of yellow having the highest lightness among the colors.

  The inventors of the present application conducted an experiment to confirm whether or not the occurrence of image defects can be suppressed by supplying toner to the cleaning blade 90. The experimental conditions are the same as in the first embodiment described above. Regarding the second embodiment, an experiment in which a continuous image forming job is performed while supplying toner to the cleaning blade 90 in the duplex printing mode, and an experiment in which a continuous image forming job is performed without supplying toner to the cleaning blade 90 in the duplex printing mode Was done.

  When a continuous image forming job was performed without supplying toner to the cleaning blade 90 in the double-sided printing mode, a streak-like image defect occurred on the recording material P on about 10,000 sheets. The cause was the same as in the first embodiment. That is, it was confirmed that the toner moved from the front side to the rear side (from the upstream side to the downstream side in the rotation direction of the secondary transfer belt 12) of the cleaning blade 90 at the position where the streak-like image defect occurred.

  On the other hand, when the continuous image forming job was performed while supplying the toner to the cleaning blade 90 in the double-sided printing mode, no image defect occurred even when the image formation was repeatedly performed on 20,000 sheets of the recording material P. When the edge portion 90a was enlarged and examined with a microscope, it was found that some wax was accumulated, but the height was 2 μm or less. When a developer containing a toner having a small average particle size was used, it was confirmed that the wax lumps were sufficiently smaller than the average particle size of the toner of 5 μm.

  As described above, in the second embodiment, the toner band 71 is formed on the upstream side in the rotation direction of the secondary transfer belt 12 immediately after the recording material P on the second surface. When the toner band 71 is formed immediately after the recording material P, the toner is supplied to the edge portion 90a immediately after the wax reaches the edge portion 90a. Then, the wax sandwiched between the edge portion 90a and the secondary transfer belt 12 is likely to be pushed to the downstream side in the rotation direction of the secondary transfer belt 12 by the toner. As a result, the wax does not remain between the edge portion 90a and the secondary transfer belt 12, and a lump of wax is less likely to be generated. Therefore, occurrence of an image defect due to the lump of wax can be suppressed.

[Third embodiment]
A third embodiment will be described with reference to FIGS. The third embodiment is employed, for example, when increasing the number of recording materials P on which an image is formed per unit time to increase productivity. That is, when increasing the number of image formations per unit time, it is necessary to increase the rotation speed of the intermediate transfer belt 40 and the secondary transfer belt 12 as the image formation speed of the image forming units PY to PK increases. For example, the rotation speed of the secondary transfer belt 12 is changed from 300 mm / sec to 400 mm / sec. Thus, when the image forming speed increases, the recording material P is transported at a higher speed. Accordingly, in the case of the first and second embodiments described above, the amount of wax that can be eliminated by the toner is smaller than the amount of wax that reaches the cleaning blade 90, so that the wax accumulated in the edge portion 90a is reduced. It gradually increases. When the amount of wax adhering to the secondary transfer belt 12 per unit time increases as described above, a lump of wax tends to be formed on the edge portion 90a. In view of this point, in the third embodiment, the two toner belts 70 and 71 are placed on the downstream side in the rotation direction of the secondary transfer belt 12 immediately before the recording material P on the second surface and upstream in the rotation direction of the secondary transfer belt 12. It is formed immediately after the recording material P on the second side on the side.

  FIG. 7 is a flowchart of the image forming process according to the third embodiment. This image forming process is executed by the control unit 200. The image forming process shown in FIG. 7 is different from the image forming process shown in FIG. 2 in that the toner band forming control (S11) is further performed after the toner band forming control (S4) and the image forming control (S5). Are different, and the description of the other processes is omitted.

  In the image forming process shown in FIG. 7, although the toner band 70 is formed immediately before the recording material P on the second side (S4), the recording on the second side after the toner image is formed (S5). The toner band 71 is also formed immediately after the material P (S11). That is, toner bands 70 and 71 are formed before and after the recording material P on the second side, respectively. FIG. 8 illustrates a toner band formed on the secondary transfer belt 12 when the image forming process according to the third embodiment is performed.

  As shown in FIG. 8, the toner belts 70 and 71 are formed on the secondary transfer belt 12 between the recording materials P (first area and second area). The toner band 70 is formed on the downstream side in the rotation direction of the secondary transfer belt 12 and immediately before (first region) the recording material P (second recording material) on the second surface. The toner band 71 is formed on the upstream side in the rotation direction of the secondary transfer belt 12 immediately after the second recording material P (a second region corresponding to a third recording material following the second recording material). . These toner bands 70 and 71 are formed in yellow having the highest lightness among the respective colors by using the same image forming portion PY as in the first embodiment.

  The inventors of the present application conducted an experiment to confirm whether or not the occurrence of image defects can be suppressed by supplying toner to the cleaning blade 90. The experimental conditions are the same as in the first embodiment described above. However, the secondary transfer belt 12 was rotated at a rotation speed of 400 mm / sec, which was faster than in the first embodiment. Regarding the third embodiment, an experiment in which a continuous image forming job is performed while supplying toner to the cleaning blade 90 in the duplex printing mode, and an experiment in which a continuous image forming job is performed without supplying toner to the cleaning blade 90 in the duplex printing mode Was done.

  When a continuous image forming job was performed without supplying toner to the cleaning blade 90 in the duplex printing mode, a streak-like image defect occurred on the recording material P on about 6,000 sheets. Further, even in the case of the first embodiment in which the toner band 70 is formed on the secondary transfer belt 12 as soon as possible on the recording material P on which the toner image is to be formed, a streak-like shape is formed on the recording material P after about 14,000 sheets. Image failure occurred. At the positions where these streak-like image defects occurred, it was confirmed that the toner moved from the front side of the cleaning blade 90 to the rear side (from the upstream side to the downstream side in the rotation direction of the secondary transfer belt 12). When the edge portion 90a was enlarged and examined with a microscope, it was found that the toner slipped along the side where the wax was deposited. When the height of the wax was measured, it was about 30 μm. Since the average particle diameter of the toner was 7 μm, the wax accumulated on the edge portion 90a to a height sufficient for the toner to pass beside the wax, and a wax mass was formed.

  On the other hand, when the continuous image forming job was performed while supplying the toner to the cleaning blade 90 in the double-sided printing mode, no image defect occurred even when the image formation was repeatedly performed on 20,000 sheets of the recording material P. When the edge portion 90a was enlarged and examined with a microscope, it was found that some wax had accumulated, but the height was 3 μm or less. It was confirmed that this wax mass was sufficiently smaller than the average particle size of the toner of 7.0 μm.

  As described above, in the third embodiment, the toner band 70 is located on the downstream side in the rotation direction of the secondary transfer belt 12 and immediately before the recording material P on the second surface, and the toner band 71 is located on the upstream side in the rotation direction of the secondary transfer belt 12 in the rotation direction. And is formed immediately after the recording material P on the second side. The toner band 70 formed immediately before the recording material P is supplied to the edge portion 90a before the wax reaches the edge portion 90a. The toner band 71 formed immediately after the recording material P is supplied immediately after the wax reaches the edge portion 90a. That is, the toner is supplied to the cleaning blade 90 before and after the wax reaches the edge portion 90a. As a result, the toner can pass the wax scraped off at the edge portion 90a, and even if the scraped wax is caught between the edge portion 90a and the secondary transfer belt 12, the wax can be pushed out. Can be. These synergistic effects make it difficult for a wax lump to be formed in the edge portion 90a, so that the occurrence of image defects due to the wax lump can be suppressed.

  In the above-described first to third embodiments, the toner bands 70 and 71 are formed with yellow having the highest brightness. This is because the toner band is formed with yellow having the highest lightness among yellow, magenta, cyan, and black, so that even if the recording material P is slightly stained by scattering of the toner, the stain is smaller than other colors. Because it is not noticeable. As shown in FIG. 1, the image forming unit PY that generates a yellow toner image is disposed at the uppermost stream in the rotation direction of the intermediate transfer belt 40 among the plurality of image forming units PY to PK. Therefore, the yellow toner image transferred to the intermediate transfer belt 40 passes through the primary transfer portion T1 formed between the remaining image forming portions PM to PK and the intermediate transfer belt 40. A bias voltage for transferring a toner image from the photosensitive drums 1M to 1K to the intermediate transfer belt 40 is applied to these primary transfer portions T1. Therefore, the yellow toner image transferred to the intermediate transfer belt 40 is charged every time it passes through the primary transfer portion T1, and the toner charge amount increases. When the toner charge amount increases, the adhesive force with the intermediate transfer belt 40 increases, and the toner hardly scatters from the toner image. The largest amount of toner charge is the yellow toner image formed by the image forming unit PY that passes the primary transfer unit T1 four times. In other words, the effect of reducing toner scattering is the highest in the yellow toner image formed by the image forming unit PY arranged at the uppermost stream in the rotation direction of the intermediate transfer belt 40, so that the toner band is also formed using yellow. I have.

[Fourth embodiment]
Incidentally, the image forming apparatus 100 can form not only a multi-color image but also a monochromatic black image. Therefore, when the black single-color mode for forming a black single-color image is designated, a black toner band is formed using the image forming unit PK. This will be described below. Here, the two toner bands 70 and 71 are printed on the second surface of the recording material P immediately downstream of the secondary transfer belt 12 in the rotation direction and on the second surface of the second transfer belt 12 in the rotation direction of the secondary transfer belt 12. The case of forming immediately after the material P will be described as an example.

  FIG. 9 is a flowchart of the image forming process according to the fourth embodiment. The image forming process illustrated in FIG. 9 is executed by the control unit 200. In FIG. 9, the same reference numerals are given to the same processes as those in the image forming process (see FIG. 7) of the third embodiment, and detailed description of those processes will be omitted.

  As shown in FIG. 9, in the single-sided printing mode (NO in S1), the control unit 200 executes image forming control for forming a toner image on the first side (front side) of the recording material P (S2, S22). It is determined whether or not the black single-color mode has been previously instructed (S21). When the black monochrome mode is instructed (YES in S21), the control unit 200 forms a toner image in black monochrome using only the image forming unit PK (S22). When the multi-color mode is instructed (NO in S21), the control unit 200 can form the first surface toner image in a plurality of colors using the image forming units PY to PK (S2).

  When it is determined that the image forming surface is not the second surface of the recording material P (NO in S3), the control unit 200 jumps to the process of S21, and forms a toner image on the first surface of the recording material P as described above ( S2, S22). When it is determined that the image forming surface is the second surface of the recording material P (YES in S3), the control unit 200 executes a toner band forming control for forming a toner band on the secondary transfer belt 12, but before that, black It is determined whether the single-color mode has been designated (S31).

  When the black monochrome mode is instructed (YES in S31), the control unit 200 forms a black toner band on the secondary transfer belt 12 between the recording materials P (S32). Here, a black toner band is formed immediately before the recording material P on the second side. Then, the control section 200 executes image forming control for forming a black toner image on the second surface of the recording material P (S33). Further, the controller 200 forms a black toner band on the secondary transfer belt 12 between the recording materials P (S34). Here, a black toner band is formed immediately after the recording material P on the second surface. When the multi-color mode is instructed (NO in S31), the control unit 200 forms yellow toner bands before and after the second recording material P (S4, S11).

  When the image forming process shown in FIG. 9 is performed, black toner bands 70 and 71 are formed in the black single-color mode, and yellow toner bands 70 and 71 are formed in the multi-color mode (see FIG. 8). The toner band 70 is formed immediately before the recording material P on the second side, and the toner band 71 is formed immediately after the recording material P on the second side.

  The amount of toner supplied to the cleaning blade 90 may be different between the multiple color mode and the black single color mode. That is, when a continuous image forming job is performed, the amount of wax for four colors in the multiple color mode and the amount of wax for one color in the black single color mode can adhere to the secondary transfer belt 12. Therefore, it is necessary to supply four times the amount of toner to the cleaning blade 90 as compared with the black single color mode in order not to generate a wax mass in the multiple color mode. For example, if the toner band length of the toner band is the same, four times the applied toner amount is required. Therefore, a toner band having a larger amount of applied toner is formed in the multi-color mode than in the black single-color mode. In this embodiment, the maximum amount of applied toner in the multi-color mode is set to 300% when the maximum amount of applied toner in the single-color mode is set to 100%. For this reason, it is preferable that the amount of applied toner in the toner band is also tripled in the multi-color mode as compared with the black single-color mode.

  The inventors of the present application conducted an experiment to confirm whether or not the occurrence of image defects can be suppressed by supplying toner to the cleaning blade 90. The experimental conditions are the same as in the first embodiment described above. However, the secondary transfer belt 12 was rotated at a rotation speed of 400 mm / sec. Regarding the fourth embodiment, an experiment was conducted in which a continuous image forming job was performed while supplying toner to the cleaning blade 90 in the double-sided printing mode, divided into a multi-color mode and a black single-color mode.

  First, experimental results in the multi-color mode will be described. In this experiment, when the yellow toner band was formed, when the black toner band was formed with the same amount of applied toner as the yellow toner band, the black toner band was formed with １ ／ of the yellow toner band. A continuous image forming job was performed separately from the case of forming.

  When a yellow toner band was formed, and when a black toner band was formed with the same amount of applied toner as the yellow toner band, image formation was repeated on 20,000 sheets of recording material P, but no image defect occurred. Was. When the edge portion 90a was enlarged and examined with a microscope, it was confirmed that some wax was accumulated, but the height was 3 μm or less, which was sufficiently smaller than the average particle diameter of the toner of 7 μm. However, when a black toner band is formed with the same amount of applied toner as the yellow toner band, when 20,000 sheets of the recording material P are stacked, it is clear that the edge portion (side surface portion) is stained with the toner. confirmed. On the other hand, in the case where the yellow toner band was formed, no smear by the toner was confirmed on the edge of the recording material P.

  In the case where the black toner band was formed with a toner amount of 1/3 of the yellow toner band, a streak-like image defect occurred on the recording material P on about 6,000 sheets. At the position where the streak-like image defect occurred, it was confirmed that the toner moved from the front side to the back side (from the upstream side to the downstream side in the rotation direction of the secondary transfer belt 12) of the cleaning blade 90. When the edge portion 90a was enlarged and examined with a microscope, it was found that the toner slipped along the side where the wax was deposited. When the height of the wax was measured, it was about 20 μm. Since the average particle diameter of the toner was 7 μm, the wax accumulated on the edge portion 90a to a height sufficient for the toner to pass beside the wax, and a wax mass was formed.

  Next, experimental results in the black monochromatic mode will be described. In this experiment, the black toner band was formed with the same amount of applied toner as the yellow toner band in the multi-color mode, and the black toner band was formed with 1/3 the applied toner amount of the yellow toner band. And a continuous image forming job was performed.

  When a black toner band was formed with the same amount of applied toner as the yellow toner band in the multi-color mode, image formation was repeated on 20,000 sheets of recording material P, but no image defects occurred. When the edge portion 90a was enlarged and examined with a microscope, it was confirmed that some wax was accumulated, but the height was 3 μm or less, which was sufficiently smaller than the average particle diameter of the toner of 7 μm. However, when 20,000 sheets of the recording material P were stacked, the edge (side surface) was stained with toner. On the other hand, when the black toner band was formed with a toner application amount of ト ナ ー of the yellow toner band, no toner stain was observed on the edge of the recording material P. This is because, when the black toner band is formed with the same amount of applied toner as the yellow toner band in the multi-color mode in the black single-color mode, an excessive amount of toner is supplied, and toner is scattered. This is because dirt is generated. On the other hand, if a black toner band is formed with a toner application amount of 1/3 of the yellow toner band, image formation can be performed without causing image defects and without causing toner smear on the edge portion. it can.

  As described above, when the black single-color mode is executed, the toner band may be formed with a smaller amount of applied toner than when the multi-color mode is executed. Can be suppressed. In addition, toner stains on the edge of the recording material P due to toner scattering are less likely to occur. Further, in the black monochrome mode, the toner band may be formed by operating the image forming unit PK, and it is not necessary to operate the other image forming units PY to PC other than the image forming unit PK, thereby extending the life of the apparatus. It becomes possible.

  In the above-described first to fourth embodiments, the toner is forcibly supplied to the edge portion 90a of the cleaning blade 90 via the secondary transfer belt 12, thereby suppressing the occurrence of an image defect due to a lump of wax. Therefore, the toner consumption tends to increase. Therefore, a measure for suppressing the toner consumption is required. In order to suppress the toner consumption, for example, there are a method of adjusting the toner formation width of the toner band and a method of adjusting the amount of applied toner of the toner band. Hereinafter, an embodiment capable of suppressing the toner consumption will be described. In order to make the description easy to understand, a case where the toner band 70 is formed immediately before the recording material P on the second side will be described as an example, but the invention is not limited thereto. That is, the present invention is applicable to a case where the toner band 70 is formed immediately after the recording material P on the second side, or a case where the toner band 70 is formed before and after the recording material P on the second side.

  FIG. 10 shows the relationship between the time transition of the amount of toner remaining on the edge portion 90 a and the toner supplied to the cleaning blade 90. As an index of the toner amount, the apparatus during image formation is temporarily stopped at a predetermined timing (every 0.5 seconds here), the cleaning blade 90 is removed, and the width of the toner remaining on the secondary transfer belt 12 (discrimination). (To be referred to as a remaining toner width). The toner band was formed with a yellow toner and a solid image of 50% of the applied toner amount over the entire length of the cleaning blade 90 in the toner band length of 5, 10 and 15 mm.

  As can be understood from FIG. 10, immediately after the supply of the toner (after 0.5 seconds), a sufficient amount of the toner remains in the edge portion 90a, but the remaining toner width gradually decreases with time. When the toner band length of the toner band is increased from, for example, 5 mm to 15 mm, the time until the remaining toner width becomes the same increases.

  The inventors of the present application conducted an experiment to check whether or not an image defect occurred when the average image ratio was changed. As an experiment, the weight ratio (T / D) of the toner and the carrier in the developer at the start of the continuous image forming job was set to 8%, the conditions such as the environment were made the same, while the average image ratio was changed. Image formation was repeatedly performed on 2,000 A3 sheets in the print mode. Here, the average image ratio is an average value of the ratio (image ratio or printing ratio) of the image area of the toner image formed on the first surface of the plurality of recording materials P to the entire area of the recording material P. .

  Table 1 shows the experimental results when the toner band was not formed. Table 1 shows, for each average image ratio, the height of the wax deposited on the edge portion 90a and whether or not a streak-like image defect has occurred on the recording material P. In addition, the case where a streak-like image defect occurred was represented by “x”.

  As can be understood from Table 1, when the average image ratio was 50% or more, a streak-like image defect occurred. When the cause was investigated, it was confirmed that the toner moved from the front side to the back side (from the upstream side to the downstream side in the rotation direction of the secondary transfer belt 12) of the cleaning blade 90 at the position where the streak-like image defect occurred. . When the edge portion 90a was enlarged and examined with a microscope, it was found that the toner slipped along the side where the wax was deposited. When the height of the wax was measured, it was about 65 μm at an average image ratio of 100% and about 20 μm at an average image ratio of 75%. Since the average particle diameter of the toner was 7 μm, the wax accumulated on the edge portion 90a of the cleaning blade 90 to a height sufficient for the toner to pass beside the wax, and a wax mass was generated.

  Table 2 shows the experimental results when the toner band was formed. However, in this experiment, image formation was repeatedly performed while changing the toner band length. In Table 2, the case where a streak-like image defect occurs is indicated by “x”.

  As can be understood from Table 2, if the toner band length of the toner band is set to 15 mm or more, it is possible to suppress the occurrence of image defects due to the wax mass regardless of the average image ratio. However, from the viewpoint of suppressing the toner consumption, it is preferable that the toner band can be formed by changing the toner band length according to the average image ratio. From the experimental results in Table 2, it is not necessary to form a toner band when the average image ratio is less than 25%. When the average image ratio is 25% or more and less than 50%, the toner band may be formed with a width of 5 mm. When the average image ratio is 50% or more and less than 75%, a toner band may be formed with a width of 10 mm. When the average image ratio is 75% or more and 100% or less, a toner band having a width of 15 mm may be formed. Thus, it is desirable to increase the toner band length as the average image ratio increases.

[Fifth Embodiment]
As described above, by forming the toner band by changing the toner band length according to the average image ratio, it is possible to suppress the occurrence of image defects due to the wax mass while suppressing the toner consumption. FIG. 11 shows specific control. FIG. 11 is a flowchart illustrating an image forming process according to the fifth embodiment. The image forming process illustrated in FIG. 11 is executed by the control unit 200. In FIG. 11, the same processes as those in the image forming process of the first embodiment (see FIG. 2) are denoted by the same reference numerals, and detailed description of those processes is omitted.

After executing the image forming control for forming the toner image on the first surface of the recording material P (S2), the control unit 200 averages the image ratio of the toner images formed on the first surface (front surface) of the plurality of recording materials P. (Average image ratio) is obtained (S41). The reason why the average image ratio of the first surface is obtained is that when the first surface of the recording material P on which the toner image is fixed comes into contact with the secondary transfer belt 12 during the secondary transfer of the second surface toner image, the secondary image This is because wax can adhere to the transfer belt 12. The average image ratio is obtained from the integrated value (video count value VC) of the digital image signal output level of each pixel per page of the recording material P. For example, the video count value VCy of the yellow image forming unit PY is an integrated value of the signal values ni _{, j} (i and j are vertical and horizontal coordinates, respectively) of each pixel constituting the image, and is calculated by Equation 1. . In Expression 1, “W” corresponds to the width of the image in the main scanning direction (corresponding to the width direction), and “h” corresponds to the width of the image in the sub-scanning direction (the rotation direction of the secondary transfer belt 12). Indicates coordinates.

[Equation 1]
VCy = n _1,1 + n _1,2 + n _1,3 + ... n _2,1 + n _2,2 + n _2,3 + ... n _{W, h}

  The final video count value VC is obtained by summing the video count values of the four colors. Then, the average image ratio is obtained by dividing the video count value VC by the area of one page of the recording material P. Here, the case where a solid image is formed over the entire area of a single color A3 size recording material P is defined as an average image ratio of 100%. If so, for example, when a solid image is formed over the entire area of the A3 size recording material P using two colors, the average image ratio becomes 200%.

  Returning to the description of FIG. 11, when it is determined that the image forming surface is the second surface (back surface) of the recording material P (YES in S3), the control unit 200 determines that the average image ratio is less than a predetermined value (for example, less than 25%). It is determined whether or not there is (S42). If the average image ratio is less than the predetermined value (YES in S42), the control unit 200 jumps to the processing in S5. Thus, when the average image ratio is less than 25% in the duplex printing mode, no toner band is formed on the secondary transfer belt 12. If the average image ratio is equal to or greater than a predetermined value (for example, equal to or greater than 25%) (NO in S42), the control unit 200 executes toner band formation control for forming a toner band on the secondary transfer belt 12 (S4). However, in this case, the control unit 200 forms a toner band having a toner band length corresponding to the average image ratio. Specifically, as described above, when the average image ratio is 25% or more and less than 50%, the width is 5 mm. When the average image ratio is 50% or more and less than 75%, the width is 10 mm. When the average image ratio is 75% or more and 100% or less, 15 mm. A toner band having a width is formed. As described above, when the toner amount of the toner image formed on the first surface is smaller than the threshold, a toner band whose toner band length is shorter than a predetermined value (for example, 15 mm) is formed.

  As described above, in the fifth embodiment, the toner band is generated by changing the length of the toner band according to the average image ratio of the toner image formed on the first surface (information on the toner amount of the image). In other words, a toner band having a toner band length capable of supplying the cleaning blade 90 with an amount of toner corresponding to the amount of wax that can exude from the toner image formed on the first surface is formed. As a result, it is possible to suppress the occurrence of image defects due to the wax mass while suppressing the toner consumption.

  As described above, the toner supplied to the cleaning blade 90 functions as a lubricant by being sandwiched between the edge portion 90a and the secondary transfer belt 12, and can pass the wax scraped off by the edge portion 90a. . However, a small amount of toner sandwiched between the edge portion 90a and the secondary transfer belt 12 can pass through the edge portion 90a, though the amount is small. Therefore, if the toner is not supplied, the toner gradually decreases as time passes ( (See FIG. 10). When an image is formed on a recording material P having a long size in the conveying direction of the recording material P, the distance between the toner bands formed on the secondary transfer belt 12 is smaller than that of the recording material P having a short size in the same direction. Becomes larger. That is, the interval at which the toner is supplied is increased. Therefore, until the toner is supplied to the cleaning blade 90, that is, while the image is formed on the recording material P, the amount of the toner sandwiched between the edge portion 90a and the secondary transfer belt 12 decreases. It becomes difficult to obtain the effect of suppressing the generation of wax lumps. In addition, fine vibration (so-called chatter) may occur in the cleaning blade 90.

  The inventors of the present application performed an experiment to check whether or not an image defect occurred when the toner band length of the toner band was changed. As an experiment, the weight ratio (T / D) of the toner and the carrier in the developer at the start of the continuous image forming job was set to 8%, and the conditions such as the image ratio and the environment were the same. The image formation was repeatedly performed on the recording material P of A3 size. Note that the image ratio was set to 200% in order to easily understand the influence of the wax. The toner band was formed with a yellow toner and a solid image of 50% of the applied toner amount over the entire length of the cleaning blade 90 in the toner band length of 5, 10 and 15 mm.

  Table 3 shows the experimental results. Table 3 shows, for each toner band length of the toner band, the height of the wax deposited on the edge portion 90a of the cleaning blade 90 and whether or not a streak-like image defect has occurred on the recording material P. In addition, the case where a streak-like image defect occurred was represented by “x”.

  As can be seen from Table 3, when the toner band length of the toner band was 10 mm or less, a streak-like image defect occurred. When the cause is investigated, it is confirmed that the toner moves from the front side to the back side (from the upstream side to the downstream side in the rotation direction of the secondary transfer belt 12) of the cleaning blade 90 at the position where the streak-like image defect occurs. Was done. When the edge portion 90a was enlarged and examined with a microscope, it was found that the toner slipped along the side where the wax was deposited. When the height of the wax was measured, it was about 15 μm when the toner band length was 10 mm, and was about 65 μm when the toner band length was 5 mm. Since the average particle diameter of the toner was 7 μm, the wax accumulated on the edge portion 90a to a height sufficient for the toner to pass alongside the wax, and a wax mass was formed.

  In addition, the inventors of the present application repeated the same image formation as in the case of the above-mentioned A3 size by changing the size of the recording material P to the A4 size. However, in order to make the image area of the toner image formed on the recording material P the same, the image was formed on 4,000 sheets of A4 size recording material P. Table 4 shows the experimental results.

  As can be understood from Table 4, when the toner band length of the toner band was 5 mm, a streak-like image defect occurred. When the height of the wax was measured, it was 63 μm, which was larger than the average particle diameter of the toner of 7 μm. In other words, it is considered that the toner has passed through the edge portion 90a and caused an image defect because the wax mass was generated at the edge portion 90a.

  As can be understood from the experimental results shown in Tables 3 and 4, if the toner band length of the toner band is set to 15 mm or more, it is possible to suppress the occurrence of image defects due to wax lumps in both A3 size and A4 size. However, if a toner band having a toner band length of 15 mm or more is always formed, toner consumption increases. Therefore, from the viewpoint of suppressing the toner consumption, it is desirable to change the toner band length of the toner band according to the size of the recording material P.

  FIG. 12 is a graph showing whether or not an image defect has occurred on a recording material P having a different size for each toner band length of the toner band. Double circles in the figure indicate that no image defect has occurred, and crosses in the figure indicate that an image defect has occurred. The time required for the A4 size recording material P to pass through the secondary transfer portion T2 (sheet passing time) is about 1.4 seconds, and the A3 size recording material P passes through the secondary transfer portion T2. It takes about 2.8 seconds.

  As shown in FIG. 12, when the remaining toner width is 0.4 mm or more in both the A4 size and the A3 size, no image defect occurs regardless of the toner band length of the toner band. That is, the remaining toner width gradually decreases over time. However, until the recording material P of A4 size or A3 size has completely passed through the secondary transfer portion T2, the remaining toner width is maintained at 0.4 mm or more, and the toner functions as a lubricant. Therefore, it is difficult to form a wax lump on the edge portion 90a.

  The time required for the recording material P to pass through the secondary transfer portion T2 is determined by the size of the recording material P (specifically, the length in the transport direction). In order to secure a residual toner width of 0.4 mm or more until the recording material P has completely passed through the secondary transfer portion T2, the toner band length of the toner band may be increased as the size of the recording material P increases. As shown in FIG. 12, a toner band having a toner band length of 10 mm may be formed for the A4 size, and a toner band having a toner band length of 15 mm may be formed for the A3 size. Here, the recording material P of A4 size and A3 size has been described as an example, but the recording material P may be of another size. Even in such a case, by changing the toner band length of the toner band in accordance with the size of the recording material P, it is possible to suppress the toner consumption and suppress the occurrence of the image defect due to the wax mass.

[Sixth embodiment]
As described above, if the toner band is formed by changing the length of the toner band according to the size of the recording material P, it is possible to suppress the toner consumption and suppress the occurrence of the image defect due to the wax mass. FIG. 13 shows specific control. FIG. 13 is a flowchart illustrating an image forming process according to the sixth embodiment. The image forming process illustrated in FIG. 13 is executed by the control unit 200. In FIG. 13, the same processes as those in the image forming process of the first embodiment (see FIG. 2) are denoted by the same reference numerals, and detailed description of those processes is omitted. Further, in order to make the explanation easy to understand, an example in which A4 size and A3 size recording materials P are used will be described.

  When it is determined that the image forming surface is the second surface (back surface) of the recording material P (YES in S3), the control unit 200 determines the toner band length according to the size of the recording material P (S51). The size of the recording material P is specified, for example, by the user operating the operation unit 201 when the user instructs the operation unit 201 to start executing a continuous image forming job. Then, the toner band length is determined to a width determined in advance for each size. The toner band length for each size is stored in the memory or the like of the control unit 200 in advance. When executing the toner band formation control (S4), the control unit 200 controls the image forming apparatus 100 to form a toner band having the determined toner band length on the secondary transfer belt 12. As described above, the toner band length is changed according to the size of the recording material P. Specifically, a toner band having a width of 10 mm for the A4 size and a width of 15 mm for the A3 size are formed.

  As described above, in the sixth embodiment, the toner band can be generated by changing the toner band length according to the size of the recording material P. That is, as the size of the recording material P is larger, a larger toner image can be formed on the first side. In this case, the toner including a toner amount that can correspond to the amount of wax that can permeate from the toner image formed on the first side. A toner band can be formed with a band length. As a result, it is possible to suppress the occurrence of image defects due to the wax mass while suppressing the toner consumption.

  Further, in view of achieving both suppression of toner consumption and suppression of occurrence of image defects, not only changing the toner band length of the toner band according to the size of the recording material P, but also changing the size of the recording material P The applied toner amount of the toner band may be changed accordingly. The point is that the amount of toner supplied to the cleaning blade 90 can be adjusted.

  FIG. 14 shows the relationship between the amount of applied toner in the toner band and the change over time in the amount of toner in the edge portion 90a. As an index of the toner amount, the width of the toner remaining on the secondary transfer belt 12 (the remaining toner width) was measured as described above. The toner band had a toner band length of 5 mm, and was formed with a solid image of 50%, 75%, and 100% of the applied toner amount of yellow toner over the entire area in the longitudinal direction of the cleaning blade 90, respectively.

  As can be understood from FIG. 14, immediately after the supply of the toner (after 0.5 seconds), a sufficient amount of the toner remains in the edge portion 90a, but the residual toner width gradually decreases with time. When the amount of applied toner in the toner band is increased, for example, from 50% to 100%, the time until the remaining toner width becomes the same increases.

  The inventors of the present application conducted an experiment to check whether or not an image defect occurred when the amount of applied toner in the toner band was changed. As an experiment, the weight ratio (T / D) of the toner and the carrier in the developer at the start of the continuous image forming job was set to 8%, and the conditions such as the image ratio and the environment were the same. The image formation was repeatedly performed on the recording material P of A3 size. Note that the image ratio was set to 200% in order to easily understand the influence of the wax.

  Table 5 shows the experimental results. Table 5 shows the height of the wax deposited on the edge portion 90a and whether or not a streak-like image defect has occurred on the recording material P for each amount of applied toner in the toner band. In addition, the case where a streak-like image defect occurred was represented by “x”.

  As can be understood from Table 5, when the amount of applied toner in the toner band was 75% or less, a streak-like image defect occurred. When the cause is investigated, it is confirmed that the toner moves from the front side to the back side (from the upstream side to the downstream side in the rotation direction of the secondary transfer belt 12) of the cleaning blade 90 at the position where the streak-like image defect occurs. Was done. When the edge portion 90a was enlarged and examined with a microscope, it was found that the toner slipped along the side where the wax was deposited. When the height of the wax was measured, it was about 21 μm when the applied toner amount was 75%, and was about 80 μm when the applied toner amount was 50%. Since the average particle diameter of the toner was 7 μm, the wax accumulated on the edge portion 90a to a height sufficient for the toner to pass alongside the wax, and a wax mass was formed.

  Further, the inventors of the present application set the size of the recording material P to the A4 size, and repeatedly performed image formation similar to the A3 size described above. However, in order to make the image area of the toner image formed on the recording material P the same, the image was formed on 4,000 sheets of A4 size recording material P. Table 6 shows the experimental results.

  As can be understood from Table 6, when the amount of applied toner in the toner band was 50% or less, a streak-like image defect occurred. When the height of the wax was measured, it was 79 μm, which is larger than the average particle diameter of the toner of 7 μm. In other words, it is considered that the toner has passed through the edge portion 90a and caused an image defect because the wax mass was generated at the edge portion 90a.

  As can be understood from the experimental results shown in Tables 5 and 6, if the amount of applied toner in the toner band is set to 100% or more, it is possible to suppress the occurrence of image defects due to the wax lumps in both the A3 size and the A4 size. However, if a toner band in which the applied amount of toner is always 100% is formed, the amount of consumed toner increases. Therefore, from the viewpoint of suppressing the toner consumption, it is desirable to change the amount of applied toner in the toner band according to the size of the recording material P.

  FIG. 15 is a graph showing whether or not an image defect has occurred on a recording material P having a different size for each amount of applied toner in the toner band. Double circles in the figure indicate that no image defect has occurred, and crosses in the figure indicate that an image defect has occurred.

  As shown in FIG. 15, when the remaining toner width is 0.4 mm or more in both the A4 size and the A3 size, no image defect occurs regardless of the amount of applied toner in the toner band. That is, the remaining toner width gradually decreases over time. However, until the recording material P of A4 size or A3 size has completely passed through the secondary transfer portion T2, the remaining toner width is maintained at 0.4 mm or more, and the toner functions as a lubricant. Therefore, it is difficult to form a wax lump on the edge portion 90a.

  The time required for the recording material P to pass through the secondary transfer portion T2 is determined by the size of the recording material P (the length in the transport direction). Here, the time is about 1.4 seconds for the A4 size, and about 2.8 seconds for the A3 size. In order to secure a residual toner width of 0.4 mm or more until the recording material P has completely passed through the secondary transfer portion T2, it is necessary to increase the amount of applied toner in the toner band as the size of the recording material P increases. is there. As shown in FIG. 15, a toner band having a toner application amount of 75% may be formed in the A4 size, and a toner band having a toner application amount of 100% may be formed in the A3 size.

[Seventh embodiment]
As described above, by forming the toner band by changing the amount of applied toner according to the size of the recording material P, it is possible to suppress the occurrence of image defects due to the wax mass while suppressing the toner consumption. FIG. 16 shows specific control. FIG. 16 is a flowchart illustrating an image forming process according to the seventh embodiment. The image forming process illustrated in FIG. 16 is executed by the control unit 200. Note that the image forming process of the seventh embodiment is the same as the image forming process of the sixth embodiment (see FIG. 13) except that the process of S61 shown in FIG. 16 is the same. Further, in order to make the explanation easy to understand, an example in which A4 size and A3 size recording materials P are used will be described.

  When it is determined that the image forming surface is the second surface (back surface) of the recording material P (YES in S3), the control unit 200 determines the amount of applied toner according to the size of the recording material P (S61). The size of the recording material P is specified, for example, by the user operating the operation unit 201 when the user instructs the operation unit 201 to start executing a continuous image forming job. Then, a predetermined toner band length is determined for each size. The amount of applied toner for each size is stored in a memory or the like of the control unit 200 in advance. When executing the toner band formation control (S4), the control unit 200 controls the image forming apparatus 100 to form a toner band on the secondary transfer belt 12 with the determined amount of applied toner. Thus, the amount of applied toner is changed according to the size of the recording material P. Specifically, a toner band is formed with a toner application amount of 75% for the A4 size and 100% for the A3 size.

  As described above, in the seventh embodiment, the toner band can be generated by changing the amount of applied toner according to the size of the recording material P. In other words, a larger toner image can be formed on the first side as the size of the recording material P is larger. In this case, the toner band amount can correspond to the amount of wax that can permeate from the toner image formed on the first side. Can be formed. As a result, it is possible to suppress the occurrence of image defects due to the wax mass while suppressing the toner consumption. However, if the amount of applied toner is too large, the cleaning blade 90 cannot completely clean the toner band itself, which may cause an image defect, and the possibility of toner scattering is high. Therefore, it is preferable to change the toner band length. . By changing both the toner band length of the toner band and the amount of applied toner according to the size of the recording material P, it is possible to achieve both suppression of toner consumption and suppression of occurrence of image defects.

  In the first to seventh embodiments described above, the toner band is formed over the entire area in the longitudinal direction of the cleaning blade 90 abutting on the secondary transfer belt 12. However, in the edge portion 90a, wax accumulates at a position corresponding to the position (area) of the recording material P on the first surface on which the toner image is formed. Therefore, from the viewpoint of suppressing the toner consumption, the toner band is not formed over the entire area in the longitudinal direction of the cleaning blade 90, and only the portion corresponding to the position (area) of the recording material P on the first surface on which the toner image is formed is formed. It is desirable to form a toner band on the surface. Further, it is desirable to determine whether or not to form a toner band according to the image ratio of the recording material P on the first side. The details will be described below.

[Eighth Embodiment]
FIG. 17 is a flowchart illustrating an image forming process according to the eighth embodiment. The image forming process illustrated in FIG. 17 is executed by the control unit 200. In FIG. 17, the same processes as those in the image forming process of the first embodiment (see FIG. 2) are denoted by the same reference numerals, and detailed description of those processes is omitted.

  After executing image forming control for forming a toner image on the first surface (front surface) of the recording material P (S2), the control unit 200 forms an image on the first surface recording material P and the image ratio of the first surface recording material P. The length of the obtained image in the sub-scanning direction is obtained (S71). The obtained image ratio and the length of the image in the sub-scanning direction are stored in a memory or the like of the control unit 200 for each recording material P. As described above, the reason for obtaining the image ratio of the first surface is that the first surface of the recording material P on which the toner image is fixed comes into contact with the secondary transfer belt 12 during the secondary transfer of the second surface toner image. This is because wax adheres to the secondary transfer belt 12 from an image. The image ratio is obtained from the integrated value (video count value VC) of the digital image signal output level of each pixel per page of the recording material P.

In the present embodiment, the video count value VC in one page is divided into eight regions in the main scanning direction of the image, and the video count values VC _{1 to} VC ₈ for each of the regions are obtained. The video count values VC _{1 to} VC ₈ are integrated values of signal values ni _{, j} (i and j are vertical and horizontal coordinates, respectively) of the pixels constituting each image of one page × eight divisions, and are calculated by Equation 2. Can be In Equation 2, “W” indicates coordinates corresponding to the width in the main scanning direction of each of the eight divided images, and “h” indicates coordinates corresponding to the width in the sub-scanning direction of each of the eight divided images. Here, the case where the video count value VC in one page is divided into eight in the main scanning direction of the image has been described as an example. However, the present invention is not limited to this. From the viewpoint of suppressing the toner consumption, the division is performed more finely. Is preferred.

[Equation 2]
VC ₁ = n _1,1 + n _1,2 + n _1,3 + ... n _2,1 + n _2,2 + n _2,3 + ... n _{W, h}
VC ₂ = n _1,1 + n _1,2 + n _1,3 + ... n _2,1 + n _2,2 + n _2,3 + ... n _{W, h}
VC ₃ = n _1,1 + n _1,2 + n _1,3 + ... n _2,1 + n _2,2 + n _2,3 + ... n _{W, h}
VC ₄ = n _1,1 + n _1,2 + n _1,3 + ... n _2,1 + n _2,2 + n _2,3 + ... n _{W, h
VC 5 = n 1,1 + n 1,2} + n 1,3 + ··· n 2,1 + n 2,2 + n 2,3 + ··· n W, h
VC ₆ = n _1,1 + n _1,2 + n _1,3 + ... n _2,1 + n _2,2 + n _2,3 + ... n _{W, h}
VC ₇ = n _1,1 + n _1,2 + n _1,3 + ... n _2,1 + n _2,2 + n _2,3 + ... n _{W, h}
VC ₈ = n _1,1 + n _1,2 + n _1,3 + ... n _2,1 + n _2,2 + n _2,3 + ... n _{W, h}

The final video count value VC ₁ to Vc ₈ is determined by the respective video count value of four colors are summed. Then, the image ratio is calculated by dividing the area of the recording material P in the video count value VC ₁ ~VC _{8 8} divided within each region. For example, if the width of the image in the main scanning direction is 324 mm and the image is divided into eight, the width of each of the eight divided regions in the main scanning direction is 40.5 mm. Therefore, the area of the recording material P in each area is “40.5 mm × the length of the recording material P in the transport direction”. However, as for the area including the end of the recording material P, “length to the end of the recording material P in the area × length of the recording material P in the transport direction” is set.

  FIG. 18 is a diagram illustrating the image ratio of each area. In FIG. 18, a solid image is formed in the entire area of AREA1 and AREA2, a solid image is formed in a half area in AREA3 and AREA5, and a solid image is formed in a quarter area in AREA4. However, the case where no image is formed on AREA6 to AREA8 is shown. When the image ratio for each area is calculated as described above, AREA1 and AREA2 are calculated as 100%, AREA3 and AREA5 are calculated as 50%, AREA4 is calculated as 25%, and AREA6 to AREA8 are calculated as 0%.

  Further, the length in the main scanning direction of the image formed on the recording material P on the first side is obtained for each of the eight divided areas. The length in the main scanning direction is, for example, 210 mm when a solid image is formed over the entire area of the A4 horizontal recording material P having a horizontal transport direction, and when the solid image is formed over the entire area of an A3 vertical recording material P having a vertical transport direction. When a solid image is formed on the entire area of the recording material P of 420 mm and B4 length, it is 364 mm.

  Returning to the description of FIG. 17, when it is determined that the image forming surface is the second surface (back surface) of the recording material P (YES in S3), the control unit 200 performs the processing of S72 to S74 for each region. The control unit 200 reads the image ratio of the recording material P on the image forming surface from the memory, and determines whether the read image ratio is less than a predetermined value (for example, less than 50%) (S72). When the image ratio is less than the predetermined value (YES in S72), the control unit 200 jumps to the processing in S5. As described above, in a region where the image ratio is less than 50%, no toner band is formed on the secondary transfer belt 12 even if a toner image is formed on the first surface.

  When the image ratio is equal to or more than a predetermined value (for example, 50% or more) (NO in S72), the control unit 200 determines whether the temporary formation width is less than a reference value (for example, 5 mm or more) (S73). If the temporary formation width is smaller than the reference value (for example, smaller than 5 mm) (YES in S73), the control unit 200 jumps to the processing in S5. Also in this case, no toner band is formed on the secondary transfer belt 12.

  When the temporary formation width is equal to or larger than the reference value (for example, 5 mm or more) (NO in S73), the control unit 200 executes toner band formation control for forming a toner band on the secondary transfer belt 12 (S74). In this case, the control unit 200 controls the image forming apparatus 100 to form a toner band on the secondary transfer belt 12 between the recording materials P. In the case of FIG. 18 described above, a toner band is formed at a portion corresponding to AREA1 to AREA3 and AREA5 where the image ratio is 50% or more, and AREA4 and AREA6 to AREA8 where the image ratio is less than 50%. No toner band is formed at the corresponding portion. That is, in this case, the toner band is formed on at least a part of the range corresponding to the recording material P in the main scanning direction (width direction). Also, for example, when a solid image is formed over the entire area of the recording material P of A3 size (420 × 297 mm), if a toner band is formed with a toner band length of 5 mm, image defects do not occur. ing. Therefore, in this embodiment, “5 mm” is set as the reference value of the toner band length. Note that the reference value is not limited to this.

  In the present embodiment, the frequency of forming the toner band is changed according to the length of the image formed on the recording material P in the sub-scanning direction. As described above, when the recording material P is the A3 size and a toner band having a toner band length of 5 mm is formed, no image failure occurs. Therefore, the length (reference length) corresponding to the A3 size is considered. It is not necessary to form a toner band until an image is formed on the recording material P. Therefore, a temporary toner band length (referred to as a temporary formation width) is calculated based on the integrated value of the length of the image in the sub scanning direction when the image ratio is 50% or more, and the temporary formation width is set to a reference value (for example, 5 mm). If the above conditions were satisfied, a toner band was formed. The tentative forming width is obtained by Expression 3. In Equation 3, “VCP” is an integrated value of the length of the image in the sub-scanning direction when the image ratio is 50% or more.

[Equation 3]
Temporary formation width = immediate previous formation width + {reference value of toner band length × VCP / reference length}

  The control unit 200 forms a toner band when the temporary formation width is equal to or more than the reference value (for example, 5 mm or more), and does not form a toner band when the temporary formation width is less than the reference value (for example, less than 5 mm) (see S73). . Then, when the toner band is formed, the control unit 200 subtracts the reference value from the temporary forming width. For example, when the first sheet of A4 horizontal recording material P on which a solid image is formed over the entire area is conveyed, even if the image ratio is 100%, the temporary formation width is 2.5 mm (5 × 210 / 420), no toner band is formed. When the second sheet is subsequently conveyed, the toner band is formed because the provisional forming width is 5.0 mm (5 × 210 × 2/420). After that, the temporary forming width becomes 0 mm by subtracting the reference value.

  For example, when the first sheet of B4 vertical recording material P on which a solid image is formed in the entire area is conveyed, the toner band is formed because the temporary forming width is 4.33 mm (5 × 364/420). Not done. When the second sheet is subsequently conveyed, the toner band is formed because the provisional forming width is 8.67 mm (5 × 364 × 2/420). Thereafter, the provisional forming width is reduced to 3.67 mm by subtracting the reference value. When the third sheet is subsequently conveyed, the temporary band is 8.00 mm “3.67+ (5 × 364/420)”, so that a toner band is formed. Thereafter, the provisional forming width becomes 3.00 mm by subtracting the reference value.

  As described above, in the eighth embodiment, the toner amount of the toner image formed on the first surface of each of the divided areas is obtained, and a toner band is formed in an area where the toner amount is larger than the threshold. As a result, the toner band can be formed only at the portion where the toner image has been formed at a high image ratio, so that it is possible to suppress the toner consumption and suppress the occurrence of the image defect due to the wax mass.

  Further, the inventors of the present application conducted an experiment for examining whether or not an image defect occurred when the toner band formation frequency and the toner band length were changed. As an experiment, the weight ratio (T / D) of the toner and the carrier in the developer at the start of the continuous image forming job was set to 8% and the conditions such as the environment were the same, while the frequency of forming the toner band and the toner band Image formation was repeatedly performed on 50,000 or more A3 sheets in the duplex printing mode while changing the length. Table 7 shows the experimental results. In Table 7, the case where a streak-like image defect occurred on the recording material P is indicated by “x”, and the number of recording materials P at that time is shown.

  As can be seen from Table 7, when the toner band length was 10 mm or less (conditions 1 to 3), streak-like image defects occurred. When the cause was investigated, it was confirmed that the toner moved from the front side to the back side (from the upstream side to the downstream side in the rotation direction of the secondary transfer belt 12) of the cleaning blade 90 at the position where the streak-like image defect occurred. . When the edge portion 90a was enlarged and examined with a microscope, it was found that the toner slipped along the side where the wax was deposited. When the height of the wax was measured, it was about 20 μm when the toner band was formed with a toner band length of 5 mm. Since the average particle diameter of the toner was 7 μm, the wax accumulated on the edge portion 90a of the cleaning blade 90 to a height sufficient for the toner to pass beside the wax, and a wax mass was generated.

  On the other hand, when the toner band length is 25 mm, if the toner formation frequency is set to each sheet (condition 4), no image defect occurs even when the image is formed on 50,000 or more recording materials P. . However, when the toner formation frequency was set every 20 sheets (condition 5), an image defect occurred on about 3,000 sheets. That is, if the toner band length is set to 25 mm and the toner formation frequency is set for each sheet, it is possible to suppress the occurrence of image defects due to the wax mass. However, in that case, the toner consumption increases.

  Thus, as shown in Condition 6, a toner band having a toner band length of 5 mm was formed for each sheet, and a toner band having a toner band length of 25 mm was formed for every 20 sheets. In this case, no image failure occurred even when an image was formed on 50,000 or more recording materials P. In the toner band having a toner band length of 5 mm, the amount of toner that can be supplied to the cleaning blade 90 is relatively small. However, if a small amount of toner can always be supplied to the edge portion 90a, the amount of toner that functions as a lubricant between the edge portion 90a and the secondary transfer belt 12 can be maintained. In this case, the wax does not remain between the edge portion 90a and the secondary transfer belt 12, so that a lump of wax hardly occurs. However, if image formation is performed continuously on a large number of recording materials P, wax may remain in some cases. The remaining wax causes wax lumps. Therefore, by forming a toner band having a toner band length of 25 mm with a relatively large amount of toner that can be supplied to the cleaning blade 90 at a predetermined timing, the wax accumulated in the edge portion 90a is washed away. Further, in this case, the amount of toner consumption is smaller than in condition 4.

[Ninth embodiment]
FIG. 19 is a flowchart illustrating an image forming process according to the ninth embodiment. This image forming process is executed by the control unit 200. The image forming process shown in FIG. 19 is different from the image forming process shown in FIG. 7 only in that the processes of S81 and S82 are added, and the detailed description of the other processes is omitted.

  As shown in FIG. 19, when the control unit 200 determines that the image forming surface is not the second surface (back surface) of the recording material P (NO in S3), it forms a toner image on the first surface (front surface) of the recording material P. Before executing the image forming control to be performed (S2), the toner band forming control is executed (S81). That is, the toner band is formed immediately before the recording material P on the first surface. The toner band formed here has a toner band length of, for example, 5 mm.

  Further, as shown in FIG. 19, when it is determined that the image forming surface is the second surface (back surface) of the recording material P (YES in S3), the control unit 200 controls the toner that forms the toner band on the secondary transfer belt 12. The band forming control is executed (S4). That is, the toner band is formed immediately before the recording material P on the second side. The toner band formed here has a toner band length of, for example, 5 mm. Further, the control unit 200 forms a toner image on the second surface of the recording material P (S5), and thereafter, the accumulated number (continuous number) of the recording material P continuously formed during the continuous image forming job is a predetermined value. It is determined whether the above is the case (for example, 20 or more) (S82). If the cumulative number of recording materials P is less than the predetermined value (NO in S82), the process proceeds to S6. If the cumulative number of recording materials P is equal to or greater than the predetermined value (YES in S82), a toner band is formed immediately after the second surface of the recording material P after the toner image is formed (S5) (S11). The toner band formed here has a toner band length of, for example, 25 mm. FIG. 20 illustrates a toner band formed on the secondary transfer belt 12 when the image forming process according to the ninth embodiment is performed.

  As shown in FIG. 20, the toner bands 80 and 81 are formed on the secondary transfer belt 12 between the recording materials P. A toner band 80 having a toner band length of 5 mm is always formed immediately before the recording material P on the first surface and immediately before the recording material P on the second surface on the downstream side in the rotation direction of the secondary transfer belt 12. On the other hand, immediately after the recording material P on the second surface on the upstream side in the rotation direction of the secondary transfer belt 12, a toner band 81 having a toner band length of 25 mm is formed at a predetermined timing (accumulated number here). That is, the toner band 80 as the first supply toner image is always formed immediately before all the recording materials on the second side. On the other hand, the toner band 81 as the second supply toner image is formed in addition to the toner band 80 when the cumulative number of the recording materials P on which the toner images are formed exceeds a threshold value.

  As described above, in the ninth embodiment, while the toner band 80 is always formed, the toner band 81 is formed only at a predetermined timing. As a result, it is possible to suppress the occurrence of image defects due to the wax mass while suppressing the toner consumption. Further, by forming the toner band 80 with a small amount of applied toner on the downstream side in the rotation direction of the secondary transfer belt 12 immediately before the recording material P on the first surface, the toner band 80 functions as a lubricant without wasting toner. Toner is always secured. This makes it difficult for the cleaning blade 90 to generate minute vibration (so-called chatter), and the toner removal performance does not decrease.

  In the above-described ninth embodiment, a toner band having a toner band length of 25 mm is formed. However, the present invention is not limited to this, and the amount of applied toner is larger than that of the toner band formed immediately before the second recording material P. A toner band may be formed. The point is that the amount of toner supplied to the cleaning blade 90 should be larger than the toner band formed immediately before the recording material P on the second side. When the cumulative value of the number of recording materials P on which images are formed during the continuous image forming job is equal to or greater than a predetermined value, the toner band length is 25 mm immediately after the second recording material P after the toner image is formed. However, the present invention is not limited to this. For example, as described above, when the average image ratio is equal to or greater than a predetermined value, or when the image ratio of the first recording material P is equal to or greater than a predetermined value, the cleaning blade 90 is disposed immediately after the second recording material P. May be formed with a large amount of toner to be supplied to the printer.

[Other embodiments]
In the first to ninth embodiments described above, the cleaning blade 90 has been described as an example of the cleaning unit. However, the present invention is not limited to this, and the cleaning unit may be an electrostatic cleaning device. FIG. 21 shows an image forming apparatus having an electrostatic secondary transfer belt cleaning device.

  The secondary transfer belt cleaning device 901 shown in FIG. 21 collects the negatively charged toner using the fur brush 91B to which the positive voltage is applied, and then removes the fur brush 92B to which the negative voltage is applied. To collect positively charged toner.

  Fur brushes 91B and 92B for electrostatic cleaning and metal rollers 91C and 92C as rubbing and rotating bodies are connected by a gear mechanism, and are driven by a drive motor (not shown) to rotate in the directions of arrows. Specifically, the fur brushes 91B and 92B rotate in the counter direction with respect to the moving direction of the secondary transfer belt 12, and rub the secondary transfer belt 12. The fur brush 92B also rotates in the counter direction with respect to the rotation direction of the metal roller 92C to rub the metal roller 92C. The fur brush 91B rotates in the whisper direction with respect to the rotation direction of the metal roller 91C to rub the metal roller 91C.

  The support roller 91A is a metal roller connected to the ground potential, rotates following the secondary transfer belt 12, and supports the secondary transfer belt 12 rubbed by the fur brush 91B. The power supply 91E applies a positive voltage to the metal roller 91C. The fur brush 91B in contact with the metal roller 91C is positively charged, and electrostatically attracts the negatively charged toner attached to the secondary transfer belt 12. The toner collected by the fur brush 91B is transferred to the metal roller 91C having a higher positive potential, and is then scraped off by the cleaning blade 91D.

  Further, the toner whose charge polarity has changed from negative polarity to positive polarity while rotating while being attached to the fur brush 91B is returned from the fur brush 91B to the secondary transfer belt 12 and then passes through the fur brush 92B. Collected by the fur brush 92B. The drive roller 23 is a metal roller covered with conductive rubber, and drives the secondary transfer belt 12 to rotate, and supports the secondary transfer belt 12 rubbed by the fur brush 92B. The power supply 92E applies a negative voltage to the metal roller 92C. The fur brush 92B in contact with the metal roller 92C is negatively charged, and electrostatically attracts the positively charged toner attached to the secondary transfer belt 12. The toner collected by the fur brush 92B is transferred to the metal roller 92C having a higher negative potential, and is then scraped off by the cleaning blade 92D.

  When double-sided printing is performed by the image forming apparatus 100A, the wax contained in the toner image transferred to the secondary transfer belt 12 of the recording material P is removed from the recording material P when the recording material P passes through the secondary transfer portion T2. It can be attached to the secondary transfer belt 12. Then, the wax attached to the secondary transfer belt 12 can be transferred to the fur brushes 91B and 92B. The wax transferred to the fur brushes 91B, 92B is scraped off by the cleaning blades 91D, 92D, and the scraped wax can accumulate and accumulate on the edges of the cleaning blades 91D, 92D. Then, the cleaning performance of the toner and the paper dust is significantly reduced. Therefore, the above-described embodiments may be applied to the case of the electrostatic secondary transfer belt cleaning device 901.

  In the above-described first to ninth embodiments, the toner belt is formed on the secondary transfer belt 12 and the toner is supplied to the cleaning blade 90 for cleaning the secondary transfer belt 12 by this. However, it is not limited to this. For example, a toner band may be formed on the intermediate transfer belt 40 so that the intermediate transfer belt 40 supplies toner to the cleaning device 45. That is, the toner band carried on the intermediate transfer belt 40 may be directly conveyed to the intermediate transfer belt cleaning device 45 without being transferred to the secondary transfer belt 12. In this case, the wax adhered to the intermediate transfer belt 40 via the secondary transfer belt 12 does not accumulate and accumulate on the edge of the intermediate transfer belt cleaning device 45. it can.

  In the above-described first to ninth embodiments, the case where the generation of the lump of wax in the cleaning blade 90 for cleaning the secondary transfer belt 12 is described, but the present invention is not limited to this. By not transferring the toner band from the intermediate transfer belt 40 to the secondary transfer belt 12, the toner may be supplied to an intermediate transfer belt cleaning device 45 that cleans the intermediate transfer belt 40. The intermediate transfer belt cleaning device 45 as a cleaning unit is not limited to a cleaning blade (see FIG. 1), and may be an electrostatic cleaning device. FIG. 22 shows an electrostatic intermediate transfer belt cleaning device.

  The intermediate transfer belt cleaning device 45A shown in FIG. 22 collects the positively charged toner by using the fur brush 192B to which a negative (the same polarity as the toner) bias voltage is applied. Thereafter, the negatively charged toner is collected by using the fur brush 191B to which a positive (positive polarity) bias voltage is applied. In the present embodiment, the fur brush 192B rubs the intermediate transfer belt 40 on the upstream side in the rotation direction of the intermediate transfer belt 40, and the fur brush 191B rubs the intermediate transfer belt 40 on the downstream side in the rotation direction of the intermediate transfer belt 40.

  The intermediate transfer belt cleaning device 45A has a first cleaning unit 191 and a second cleaning unit 192. The first cleaning unit 191 includes a fur brush 191B, a metal roller 191C, a power supply 191E, and a cleaning blade 191D. The second cleaning unit 192 includes a fur brush 192B, a metal roller 192C, a power supply 192E, and a cleaning blade 192D. The fur brushes 191B and 192B as the rotating members for removing static electricity and the metal rollers 191C and 192C as the rotating members for rubbing are connected by a gear mechanism (not shown), and are driven by a driving motor (not shown) to rotate. The fur brushes 191B and 192B rotate in a direction opposite to the rotation direction of the intermediate transfer belt 40 at a contact position with the intermediate transfer belt 40, and rub the intermediate transfer belt 40. The fur brush 191B rubs the peripheral surface of the intermediate transfer belt 40 after the fur brush 192B rubs.

  Fur brushes 191B and 192B rub against metal rollers 191C and 192C, respectively. The fur brush 191B rotates in the same direction as the rotation direction of the metal roller 191C at the contact position with the metal roller 191C, and rubs the metal roller 191C. The fur brush 192B rotates in the same direction as the rotation direction of the metal roller 192C at the contact position with the metal roller 192C, and rubs the metal roller 192C.

  The support roller 192A is a metal roller connected to the ground potential (0 V), supports the intermediate transfer belt 40 rubbed by the fur brush 192B from the inner peripheral side, and rotates following the intermediate transfer belt 40. The support roller 192A is an aluminum cylindrical roller having a diameter of, for example, 13 mm. The drive roller 43 is a metal roller connected to the ground potential (0 V), supports the intermediate transfer belt 40 rubbed by the fur brush 191B from the inner peripheral side, and rotationally drives the intermediate transfer belt 40 as described above. Let it.

  The power supply 192E applies a negative voltage to the metal roller 192C to generate an electric field between the fur brush 192B and the support roller 192A. As a result, the fur brush 192B rubbing the metal roller 192C is negatively charged, and can adsorb the positively charged toner adhering to the intermediate transfer belt 40. The toner adsorbed on the fur brush 192B is transferred to the metal roller 192C having a higher negative potential, and is scraped off by the cleaning blade 192D. The cleaning blade 192D abuts in the counter direction with respect to the rotation direction of the metal roller 192C to scrape off the toner from the metal roller 192C.

  On the other hand, the power supply 191E applies a positive voltage to the metal roller 191C to generate an electric field between the fur brush 191B and the driving roller 43. As a result, the fur brush 191B rubbing the metal roller 191C is positively charged, and can adsorb the negatively charged toner adhering to the intermediate transfer belt 40. The toner adsorbed on the fur brush 191B is transferred to the metal roller 191C having a higher positive potential, and is scraped off by the cleaning blade 191D. The cleaning blade 191D abuts in the counter direction with respect to the rotation direction of the metal roller 191C to scrape off the toner from the metal roller 191C.

  When double-sided printing is performed by the image forming apparatus 100A, the wax contained in the toner image transferred to the secondary transfer belt 12 of the recording material P is removed from the recording material P when the recording material P passes through the secondary transfer portion T2. It can be attached to the secondary transfer belt 12. Then, the wax attached to the secondary transfer belt 12 can be transferred to the fur brushes 91B and 92B. The wax transferred to the fur brushes 91B, 92B is scraped off by the cleaning blades 91D, 92D, and the scraped wax can accumulate and accumulate on the edges of the cleaning blades 91D, 92D. Then, the cleaning performance of the toner and the paper dust is significantly reduced. Therefore, the above-described embodiments may be similarly applied to the case of the electrostatic intermediate transfer belt cleaning device 45A.

  In each of the embodiments described above, the secondary transfer belt unit 56 is used. However, the present invention is not limited to this, and a secondary transfer roller may be used.

  In the present embodiment described above, a multi-color printer has been described as an example of an image forming apparatus. However, the present invention is not limited to this, and any image forming apparatus that performs secondary transfer using an intermediate transfer member may be used. Such a thing may be used. That is, any image forming apparatus that performs secondary transfer using an intermediate transfer member can be implemented without distinction between a tandem type / one drum type, a charging method, an electrostatic image forming method, a developing method, a transfer method, and a fixing method. Examples of such an image forming apparatus include a printer, various printing machines, a copying machine, a facsimile, and a multifunction peripheral.

100 (100A): image forming apparatus, 200: control unit, 1Y to 1K: image carrier (photosensitive drum), 12: secondary transfer rotating body (secondary transfer belt), 34: transport unit (reverse transport path), 35: conveyance section (double-sided conveyance path), 40: intermediate transfer member (intermediate transfer belt), 45 (45A): cleaning means (intermediate transfer belt cleaning device), 60a: heating means (heating roller), 70 (71) Supply toner image (toner band), 80: supply toner image (first supply toner image, toner band), 81: supply toner image (second supply toner image, toner band), 90: cleaning means (cleaning blade), 91B (92B, 191B, 192B): Rotating body for removing static electricity (fur brush), 91C (92C, 191C, 192C): Rotating body (metal roller), 901: Cleaning hand (Secondary transfer belt cleaning device), P ... recording medium, T1 ... primary transfer portion, T2 ... secondary transfer portion

An image forming apparatus according to an aspect of the invention includes an image carrier, an image forming unit configured to form a toner image on the image carrier by using a toner including wax, and an image carrier that contacts the image carrier. A transfer rotator that forms a transfer portion in the transfer portion and transfers a toner image from the image bearing member to a recording material in the transfer portion; and a rotator that transports the toner removed from the transfer rotator or the transfer rotator. , A blade capable of removing toner on the transfer rotating body or the rotating body, a fixing device for heating and fixing a toner image formed on the recording material, and a recording material passing through the fixing device A transport unit that reverses the front and back and transports to the transfer unit, and in a double-sided printing mode in which toner images are formed on both surfaces of a plurality of recording materials, the second recording material following the preceding first recording material, Transfer at transfer section Based on the information as to whether the surface to be printed is the second surface, in a region corresponding to between the first recording material and the second recording material, so as to form a supply toner image for supplying to the blade. And a control unit for controlling the image forming unit.

In the image forming section PY, a yellow toner image is formed on the photosensitive drum 1Y and is primarily transferred to the intermediate transfer belt 40. In the image forming section PM, a magenta toner image is formed on the photosensitive drum 1M and is transferred so as to overlap the yellow toner image on the intermediate transfer belt 40. In the image forming units PC and PK, a cyan toner image and a black toner image are formed on the photosensitive drums 1C and 1K, respectively, and sequentially transferred onto the intermediate transfer belt 40. The intermediate transfer belt 40 as an image carrier rotates while carrying the toner image.

100 (100A): image forming apparatus, 200: control unit, 1Y to 1K: image carrier (photosensitive drum), 12: secondary transfer rotating body (secondary transfer belt), 34: transport unit (reverse transport path), 35: conveying section (double-sided conveying path), 40: image carrier ( intermediate transfer body , intermediate transfer belt), 45 (45A): cleaning means (intermediate transfer belt cleaning device), 60a: heating means (heating roller), 70 (71) ... supply toner image (toner band), 80 ... supply toner image (first supply toner image, toner band), 81 ... supply toner image (second supply toner image, toner band), 90 ... cleaning means (cleaning) Blades), 91B (92B, 191B, 192B): Static elimination rotating body (fur brush), 91C (92C, 191C, 192C): Sliding rotating body (metal roller), 901: Clear Training means (secondary transfer belt cleaning device), P ... recording medium, T1 ... primary transfer portion, T2 ... secondary transfer portion

Claims (8)

An image carrier;
An image forming unit that develops a toner image on the image carrier using a toner containing wax;
A transfer rotator that forms a transfer portion between the image carrier and the image carrier in contact with the image carrier, and transfers a toner image from the image carrier to a recording material at the transfer portion;
The transfer rotator, or a blade capable of removing the toner on the transfer rotator or the rotator by contacting the rotator that conveys the toner removed from the transfer rotator,
A fixing device that heats and fixes the toner image formed on the recording material;
A transport unit that reverses the front and back of the recording material that has passed the fixing device and transports the recording material to the transfer unit,
In a two-sided printing mode in which toner images are formed on both surfaces of a plurality of recording materials, regarding a second recording material subsequent to the preceding first recording material, whether or not the surface to be transferred in the transfer unit is the second surface Based on the information, in a region corresponding to between the first recording material and the second recording material, a control unit that controls the image forming unit to form a supply toner image to be supplied to the blade, Prepare,
An image forming apparatus comprising: The control unit forms the supply toner image based on information on a toner amount of an image formed on the first surface of the second recording material,
The image forming apparatus according to claim 1, wherein: The control unit forms the supply toner image when the toner amount or the image ratio of the toner image formed on the first surface of the second recording material is larger than a threshold,
The image forming apparatus according to claim 1, wherein: The control unit is configured to determine whether a surface on which the second recording material is transferred in the transfer unit is a second surface, and information on a toner amount of an image formed on the first surface of the second recording material. A first area corresponding to the first recording material and the second recording material and a third area corresponding to the second recording material and the third recording material subsequent to the second recording material. And controlling the image forming unit to form the supply toner image in each of the second area and
The image forming apparatus according to claim 1, wherein: The supply toner image is formed over the entire area where the blade abuts in a width direction crossing the rotation direction of the rotating body.
The image forming apparatus according to claim 1, wherein: The image carrier is an intermediate transfer belt provided with an elastic layer on the surface,
The image forming apparatus according to claim 1, wherein: The transfer rotator is a secondary transfer belt,
The image forming apparatus according to claim 1, wherein: A fur brush for electrostatically cleaning the transfer rotating body,
The rotating body contacts the fur brush and collects toner from the fur brush,
The image forming apparatus according to claim 1, wherein:

Images