Image forming apparatus

Abstract

To prevent faulty cleaning of a discharge toner band, while preventing a reduction in productivity.SOLUTION: An image forming apparatus 100 has: a cleaning blade 82 that is in contact with an image carrier 7 along a second direction substantially orthogonal to a first direction being the direction of movement of a surface of the image carrier 7 and removes toner from the image carrier 7; and a control unit 200 that controls to execute a predetermined operation to form a predetermined toner image not transferred to a recording material S on the image carrier 7 based on an index value correlated with the printing rate of a toner image formed on the image carrier 7. The predetermined toner image has a configuration in which a printing part extending along the first direction and a non-printing part extending along the first direction and adjacent to the printing part are repeatedly formed, when seen per unit area of 1 mm in the first direction and the second direction within at least a predetermined range of a leading end part in the first direction.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, such as a copying machine, a printer, a facsimile machine, or a multifunction machine having a plurality of the functions of these machines, which uses an electrophotographic system or an electrostatic recording system. [Background technology]

[0002] Conventionally, in image forming apparatuses using electrophotography or the like, a cleaning device is used to remove deposits such as toner (residual toner) remaining on an image carrier such as a photosensitive drum or intermediate transfer belt after a toner image is transferred from the image carrier to a transferee. A widely used cleaning device has a structure in which a cleaning blade made of a plate-shaped elastic member as a cleaning member is brought into contact with the surface of the image carrier, and the cleaning blade scrapes off deposits such as residual toner from the surface of the rotating image carrier.

[0003] In such a cleaning device, the toner reaches the edge of the cleaning blade, and the components of the toner and the external additives of the toner penetrate into the blade nip, which is the contact portion (nip portion) between the cleaning blade and the image carrier. This provides a lubricating effect between the cleaning blade and the image carrier, and favorable cleaning performance can be obtained. However, if the amount of toner that reaches the edge of the cleaning blade continues to be small, the slippage between the cleaning blade and the image carrier becomes poor, and the cleaning blade may vibrate finely, generating abnormal noises such as chattering and squealing, or the cleaning blade may turn over. In addition, when it is necessary to slow down the conveying speed of the recording material, slowing down the rotation speed of the image carrier may easily cause the slippage between the cleaning blade and the image carrier to become poor.

[0004] In response to this, Patent Document 1 describes a technique for forming a toner band on the photosensitive drum that is not transferred to the recording material based on the result of judging the level of lubricity between the cleaning blade and the photosensitive drum. This predetermined toner image for providing lubricity between the cleaning blade and the image carrier by supplying toner that acts as a lubricant to the edge of the cleaning blade is referred to as a "lubricating toner band" here.

[0005] On the other hand, in an image forming apparatus using an electrophotographic method or the like, if a low-print-ratio image, which is an image with a low print ratio, is continuously formed, the toner consumed from the developing device decreases, and the charging performance and fluidity of the toner may decrease. This is because the external additives for charge control and fluidity control added to the toner are peeled off from the toner base or embedded in the surface of the toner base due to friction between the toner and the developer carrier, a stirring member, a regulating member, and other members of the developing device. Therefore, if a low-print-ratio image is continuously formed, the amount of toner with reduced charging performance and fluidity (herein also referred to as "deteriorated toner") increases in the developing device (on the developer carrier or in the developing container), and toner scattering, fogging (adhesion of toner to non-image areas), and the like may easily occur.

[0006] In response to this, Patent Document 2 describes the following technology to prevent toner from remaining in the developing device for a long time. That is, for each image formation, if an index value (video count value) of the toner consumption amount is smaller than a predetermined threshold value, the difference between the threshold value and the index value is calculated. Then, when an integrated value obtained by accumulating the calculated difference reaches a predetermined value, a toner band that is not transferred to the recording material is formed, and toner is forcibly discharged (consumed) from the developing device. This predetermined toner image for discharging toner from the developing device when a low printing rate image is continuously formed is referred to here as a "discharged toner band." [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2007-304371 A [Patent Document 2] JP 2011-48083 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, in recent years, the fluidity of the toner has tended to increase due to the toner being made substantially spherical in order to improve image quality. When the fluidity of the toner increases, if the toner is excessively supplied to the edge of the cleaning blade, the toner cannot be scraped off by the cleaning blade and slips through the cleaning blade, which tends to cause cleaning defects. The lubricating toner band and the spit toner band described above are generally solid images covering substantially the entire image forming area in a direction substantially perpendicular to the moving direction of the surface of the image carrier, so that a large amount of toner is supplied to the edge of the cleaning blade per unit time. Therefore, if the lubricating toner band or the spit toner band supplies excessive toner to the edge of the cleaning blade, cleaning defects may occur.

[0009] In particular, since a sufficient amount of toner needs to be discharged from the developing device to form the spit toner band, the amount of toner in the spit toner band is generally greater than the amount of toner in the lubricating toner band. However, in order to prevent an increase in downtime (a period during which images cannot be output) due to the operation of forming the spit toner band and to prevent a decrease in productivity, it is not preferable to simply make the spit toner band a halftone image.

[0010] Therefore, one object of the present invention is to suppress poor cleaning of the spit toner band while suppressing a decrease in productivity. [Means for solving the problem]

[0011] The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides an image forming device including a rotatable image carrier carrying a toner image, a developing device for developing an electrostatic image with toner, and an image forming means for forming a toner image on the image carrier, a transfer means for transferring the toner image formed on the image carrier to a recording material, a cleaning blade that comes into contact with the image carrier along a second direction substantially perpendicular to a first direction that is the moving direction of the surface of the image carrier and removes toner from the image carrier, and a cleaning device that removes a predetermined toner image that is not transferred to the recording material from the image carrier based on an index value that correlates with the printing rate of the toner image formed on the image carrier. and a control unit that controls the cleaning blade to execute a predetermined operation of forming a predetermined toner image on an image carrier along the second direction and removing the predetermined toner image from the image carrier by the cleaning blade, wherein the predetermined toner image is formed by repeating printed portions extending along the first direction and non-printed portions extending along the first direction adjacent to the printed portions, at least within a predetermined range of the tip end in the first direction, when viewed per unit area of ​​1 mm in each of the first direction and the second direction.

[0012] According to another aspect of the present invention, there is provided a developing device for developing an electrostatic image with toner, the developing device including: an image forming unit for forming a toner image on the image carrying member; a transfer unit for transferring the toner image formed on the image carrying member to a recording material; a cleaning blade for contacting the image carrying member along a second direction substantially perpendicular to a first direction which is a moving direction of the surface of the image carrying member and removing toner from the image carrying member; a first operation for forming a predetermined first toner image on the image carrying member along the second direction which is not transferred to the recording material, and removing the first toner image from the image carrying member by the cleaning blade; and a second operation for forming a predetermined second toner image on the image carrying member along the second direction which is not transferred to the recording material, and removing the second toner image by the cleaning blade. and a control unit that controls the first toner image to be removed from the image carrier by a second operation, wherein the first toner image is formed, at least in a predetermined range of the tip end in the first direction, when viewed per unit area of ​​1 mm in each of the first direction and the second direction, by repeating printed portions extending along the first direction and non-printed portions extending along the first direction adjacent to the printed portions, and the second toner image is formed, at least in a predetermined range of the tip end in the first direction, when viewed per unit area of ​​1 mm in each of the first direction and the second direction, by repeating printed portions extending along the second direction and non-printed portions extending along the second direction adjacent to the printed portions.

[0013] According to another aspect of the present invention, there is provided an image forming apparatus including a rotatable image carrier carrying a toner image, and a developing device for developing an electrostatic image with toner, the image forming apparatus including: an image forming means for forming a toner image on the image carrier; a transfer means for transferring the toner image formed on the image carrier to a recording material; a cleaning blade that comes into contact with the image carrier along a second direction substantially perpendicular to a first direction that is a moving direction of the surface of the image carrier and removes toner from the image carrier; and a toner image forming device that forms a predetermined toner image on the image carrier along the second direction based on an index value that correlates with a printing rate of the toner image formed on the image carrier, the predetermined toner image being not transferred to the recording material. and a control unit that controls the cleaning blade to execute a predetermined operation of removing the toner from the image carrier, wherein the predetermined toner image is formed in a predetermined range at least at the tip end in the first direction, when viewed per unit area of ​​1 mm in each of the first direction and the second direction, at a density higher than the average density of the unit area, and is formed by repeatedly forming a high-density printed portion extending along the first direction and a low-density printed portion having a density lower than the average density of the unit area, the low-density printed portion extending along the first direction adjacent to the high-density printed portion. Effect of the Invention

[0014] According to the present invention, it is possible to suppress poor cleaning of the spit toner band while suppressing a decrease in productivity. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Diagram 2] FIG. 2 is a schematic cross-sectional view of a developing device. [Diagram 3] FIG. 2 is a schematic cross-sectional view of a belt cleaning device. [Figure 4] FIG. 2 is a schematic block diagram showing a control mode of the image forming apparatus. [Diagram 5] FIG. 11 is a flowchart of a control process for determining whether or not a lubricating toner band forming operation is required. [Figure 6]FIG. 11 is a flowchart of a control process for determining whether or not a discharge toner band forming operation is required. [Figure 7] 1A and 1B are schematic diagrams illustrating a mechanism by which poor cleaning of a toner band occurs. [Figure 8] 11 is a graph showing the distortion of a cleaning blade when poor cleaning of a toner band occurs. FIG. [Figure 9] 5A and 5B are schematic diagrams for explaining a pattern of a lubricating toner band. [Figure 10] 5A and 5B are schematic diagrams for explaining a pattern of ejected toner bands. [Figure 11] FIG. 4 is a graph showing the charge amount of toner in a toner band. [Figure 12] 10A and 10B are schematic diagrams showing other examples of toner band patterns. [Figure 13] FIG. 11 is a schematic block diagram showing a control mode of another example of the image forming apparatus. [Figure 14] FIG. 11 is a flow chart of control for changing the pattern of the ejected toner band. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

[0017] [Example 1] 1. Overall configuration and operation of the image forming apparatus 1 is a schematic cross-sectional view of an image forming apparatus 100 according to this embodiment. The image forming apparatus 100 according to this embodiment is a tandem type laser beam printer that employs an intermediate transfer method and is capable of forming a full-color image using an electrophotographic method.

[0018] Image forming apparatus 100 has a plurality of image forming units (stations), namely, first, second, third and fourth image forming units PY, PM, PC and PK which form images of yellow (Y), magenta (M), cyan (C) and black (K), respectively. The first, second, third and fourth image forming units PY, PM, PC and PK are arranged in a straight line in the stated order along the moving direction of the image transfer surface of intermediate transfer belt 7, which will be described later. Note that elements having the same or corresponding functions or configurations provided for each color may be generally described by omitting Y, M, C or K at the end of the reference numerals indicating that the element is for any one of the colors. In this embodiment, the image forming unit P (PY, PM, PC, PK) is configured to include photosensitive drums 1 (1Y, 1M, 1C, 1K), charging rollers 2 (2Y, 2M, 2C, 2K), developing devices 4 (4Y, 4M, 4C, 4K), primary transfer rollers 5 (5Y, 5M, 5C, 5K), drum cleaning devices 6 (6Y, 6M, 6C, 6K), etc., which will be described later.

[0019] The photosensitive drum 1, which is a rotatable drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) serving as a first image carrier, is rotated at a predetermined peripheral speed (process speed) in the direction of arrow R1 (clockwise direction) in FIG. 1. The surface of the rotating photosensitive drum 1 is charged substantially uniformly to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by a charging roller 2, which is a roller-type charging member serving as a charging means. The charging roller 2 is disposed in contact with the surface of the photosensitive drum 1 and rotates in accordance with the rotation of the photosensitive drum 1. During charging, a predetermined charging voltage (charging bias) containing a DC component of the same polarity as the charging polarity (negative polarity in this embodiment) of the photosensitive drum 1 is applied to the charging roller 2 by a charging power source (not shown) serving as a charging voltage application means. Note that a minute gap is formed between the photosensitive drum 1 and the charging roller 2 on the upstream side and downstream side of the contact portion between the photosensitive drum 1 and the charging roller 2 in the rotation direction of the photosensitive drum 1. The charging roller 2 charges the surface of the photosensitive drum 1 by discharging generated in at least one of the gaps on the upstream side and the downstream side.

[0020] The surface of the charged photosensitive drum 1 is scanned and exposed to laser light L based on image information by an exposure device (laser scanner) 3 as an exposure means, and an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 1.

[0021] The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) by supplying developer toner by the developing device 4 as a developing means, and a toner image (toner image, developer image) is formed on the photosensitive drum 1. The developing device 4 has a developing sleeve 41 as a developer carrier (developing member) that carries the developer and transports it to a portion facing the photosensitive drum 1. During development, a predetermined developing voltage (developing bias) containing a DC component of the same polarity as the charging polarity (negative polarity in this embodiment) of the photosensitive drum 1 is applied to the developing sleeve 41 by a developing power source (not shown) as a developing voltage application means. In this embodiment, an oscillating voltage in which a DC voltage and an AC voltage are superimposed is applied to the developing sleeve 41 as the developing voltage. In this embodiment, a toner image is formed by image portion exposure and reversal development. That is, toner charged to the same polarity (negative polarity in this embodiment) as the charging polarity of the photosensitive drum 1 adheres to the exposed portion (image portion) on the photosensitive drum 1, the absolute value of the potential of which has been reduced by being exposed after being charged approximately uniformly. In this embodiment, the normal charging polarity of the toner, which is the main charging polarity of the toner during development, is negative. The developing device 4 will be described in further detail later.

[0022] An intermediate transfer belt 7, which is an intermediate transfer body formed of an endless belt as a second image carrier, is disposed so as to face the four photosensitive drums 1. The intermediate transfer belt 7 is stretched around a plurality of support rollers (tension rollers) 71 to 74, and tensioned with a predetermined tension. The intermediate transfer belt 7 rotates (moves around) in the direction of arrow R2 (counterclockwise direction) in FIG. 1 at a circumferential speed (process speed) corresponding to the circumferential speed of the photosensitive drum 1, by transmitting a driving force when a driving roller 71, which is one of the plurality of support rollers, is rotated. Primary transfer rollers 5Y, 5M, 5C, and 5K, which are roller-type primary transfer members as primary transfer means, are disposed on the inner circumferential surface (back surface) side of the intermediate transfer belt 7, corresponding to each of the photosensitive drums 1Y, 1M, 1C, and 1K. The primary transfer roller 5 is pressed against the photosensitive drum 1 via the intermediate transfer belt 7, and forms a primary transfer portion (primary transfer nip portion) T1 where the intermediate transfer belt 7 and the photosensitive drum 1 come into contact with each other. The toner image formed on the photosensitive drum 1 is transferred (primary transfer) onto the intermediate transfer belt 7, which is a rotating transfer target, at the primary transfer portion T1 by the action of the primary transfer roller. During the primary transfer, a predetermined primary transfer voltage (primary transfer bias) of a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) is applied to the primary transfer roller 5 by a primary transfer power source (not shown) as a primary transfer voltage application means. For example, when a full-color image is formed, the toner images of the colors Y, M, C, and K formed on each photosensitive drum 1 are transferred sequentially at each primary transfer portion T1 so as to be superimposed on the intermediate transfer belt 7. In this embodiment, each image forming portion P constitutes an image forming means for forming a toner image on the intermediate transfer belt 7.

[0023] A secondary transfer roller (secondary transfer outer roller) 9, which is a roller-shaped secondary transfer member serving as a secondary transfer means, is disposed at a position facing the driving roller 71 on the outer peripheral surface (surface) side of the intermediate transfer belt 7. The secondary transfer roller 9 is pressed against the driving roller 71, which functions as a facing roller (secondary transfer inner roller), via the intermediate transfer belt 7, to form a secondary transfer portion (secondary transfer nip portion) T2 where the intermediate transfer belt 7 and the secondary transfer roller 9 come into contact with each other. The toner image formed on the intermediate transfer belt 7 is transferred (secondarily transferred) onto the recording material S, which is a transfer target material that is sandwiched and conveyed between the intermediate transfer belt 7 and the secondary transfer roller 9, by the action of the secondary transfer roller 9 at the secondary transfer portion T2. ​​During the secondary transfer, a predetermined secondary transfer voltage (secondary transfer bias) of a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) is applied to the secondary transfer roller 9 by a secondary transfer power source (not shown) serving as a secondary transfer voltage application means. The recording material S is selectively sent out one by one from a cassette 12 serving as a recording material storage section by a pickup roller (feed roller) 13 serving as a feeding member, and is conveyed by a conveying roller pair 14 serving as a conveying member to a registration roller pair 15 serving as a synchronous conveying member. The cassette 12 is detachably disposed at the bottom of the device body 110 of the image forming apparatus 100. The recording material S is conveyed by the registration roller pair 15 to the secondary transfer section T2 in synchronization with the toner image on the intermediate transfer belt 7. Note that, although various materials such as plain paper, synthetic resin sheets, and envelopes can be used as the recording material S, the present embodiment will be described assuming that the recording material S is plain paper.

[0024] The recording material S onto which the toner image has been transferred is conveyed to a fixing device 10 as a fixing means. The fixing device 10 has a fixing roller 10a equipped with a heating means, and a pressure roller 10b that is in pressure contact with the fixing roller 10a. The fixing device 10 applies heat and pressure to the recording material S carrying an unfixed toner image while sandwiching and conveying the recording material S between the fixing roller 10a and the pressure roller 10b, thereby fixing (melting and fixing) the toner image onto the recording material S. The temperature of the fixing device 10 (fixing roller 10a) is determined based on the result of detection of the environmental temperature by an environmental temperature sensor (not shown) provided in the image forming apparatus 100 and the setting of the type (paper type) of the recording material S. In general, if the process speed is the same, the lower the environmental temperature and the larger the basis weight of the set paper type, the higher the temperature of the fixing device 10 is set. In this embodiment, for example, plain paper 1, plain paper 2, plain paper 3, etc. can be set as the paper type, and the basis weights of plain paper 1, plain paper 2, and plain paper 3 are respectively 64 to 75 g / m 2 , 76~90g / m 2 , 91~105g / m 2 The temperatures of the fixing device 10 set for the plain paper 1, the plain paper 2, and the plain paper 3 are 190° C., 200° C., and 210° C., respectively, when the environmental temperature is 23° C. After passing through the fixing device 10, the recording material S is discharged (output) to a discharge tray 11 provided outside the device main body 110 as a discharge section.

[0025] The surface of the photosensitive drum 1 after the primary transfer process is cleaned by a drum cleaning device 6 serving as a photosensitive body cleaning means. That is, deposits such as toner (primary transfer residual toner) that remain on the photosensitive drum 1 without being transferred onto the intermediate transfer belt 7 during the primary transfer are removed and collected from the photosensitive drum 1 by the drum cleaning device 6. The drum cleaning device 6 scrapes off deposits such as primary transfer residual toner from the surface of the rotating photosensitive drum 1 using a cleaning blade serving as a cleaning member arranged in contact with the surface of the photosensitive drum 1, and stores the deposits in a cleaning container.

[0026] In addition, a belt cleaning device 8 is disposed as an intermediate transfer body cleaning means at a position facing a tension roller 74, which is one of the multiple support rollers, on the outer peripheral surface side of the intermediate transfer belt 7. The belt cleaning device 8 may be disposed downstream of the secondary transfer portion T2 and upstream of the primary transfer portion T1 (the most upstream primary transfer portion T1Y) in the rotation direction of the intermediate transfer belt 7. The tension roller 74 is a support roller that is urged from the inner peripheral surface side of the intermediate transfer belt 7 toward the outer peripheral surface side to apply tension to the intermediate transfer belt 7. The surface of the intermediate transfer belt 7 after the secondary transfer process is cleaned by the belt cleaning device 8. That is, the toner (secondary transfer residual toner) that remains on the intermediate transfer belt 7 without being transferred to the recording material S during the secondary transfer and the adhering matter such as paper powder that adheres to the intermediate transfer belt 7 during the secondary transfer are removed from the intermediate transfer belt 7 and collected by the belt cleaning device 8. The belt cleaning device 8 scrapes off adhering matter such as secondary transfer residual toner from the surface of the rotating intermediate transfer belt 7 using a cleaning blade 82 arranged in contact with the intermediate transfer belt 7, and stores the scraped matter in a cleaning container. The belt cleaning device 8 will be described in more detail later.

[0027] Further, the developing devices 4Y, 4M, 4C, and 4K are supplied with toner by the amount equivalent to that consumed during development from toner bottles 16Y, 16M, 16C, and 16K, respectively, which serve as supply containers.

[0028] Here, the intermediate transfer belt 7 is made of a rubber material, a resin material, or the like. In this embodiment, a belt with a single layer structure made of PEEK (polyether ether ketone), a resin material, and molded into an endless shape is used as the intermediate transfer belt 7. The intermediate transfer belt 7 is made of a resin base material with carbon black dispersed therein, and has a surface resistivity of, for example, 1×10 12 [Ω / □], volume resistivity is 1×10 9The electrical resistance is adjusted to be [Ω·cm]. A lubricant is applied to the surface of the intermediate transfer belt 7 to reduce the frictional resistance of the surface during initial use. Kyna and zinc stearate are widely used as this lubricant, but zinc stearate was applied in this embodiment. By applying a mixture of powdered zinc stearate and a volatile solvent (HEF in this embodiment) at a specified ratio, zinc stearate can be applied efficiently and uniformly to the surface of the intermediate transfer belt 7.

[0029] 2. Developing device Next, a further description will be given of the developing device 4. Figure 2 is a schematic cross-sectional view of the developing device 4 in this embodiment.

[0030] In this embodiment, the developing device 4 has a developing container 42. In the developing container 42, a two-component developer containing toner (non-magnetic toner particles) and carrier (magnetic carrier particles) is contained as a developer. In addition, the developing device 4 has, in the developing container 42, a developing sleeve 41 as a developer carrier (developing member) and a brush cutter member as a regulating member for regulating the brush of the developer carried on the developing sleeve 41. In this embodiment, the developer storage section 45 inside the developing container 42 is partitioned into a developing chamber 45a and an agitating chamber 45b on the left and right in the approximately horizontal direction by a partition wall 44 extending in the approximately vertical direction to the paper surface of FIG. 2. The developer is contained in the developing chamber 45a and the agitating chamber 45b. In the developing chamber 45a and the agitating chamber 45b, a first conveying screw 46a and a second conveying screw 22b, which are agitating and conveying members as agitating and conveying means, are respectively disposed. The first conveying screw 46a is disposed at the bottom of the developing chamber 45a substantially parallel to the direction of the rotation axis of the developing sleeve 41, and conveys the developer in the developing chamber 45a in one direction along the direction of the rotation axis by rotating. The second conveying screw 46b is disposed at the bottom of the stirring chamber 45b substantially parallel to the first conveying screw 46a, and conveys the developer in the stirring chamber 45b in the opposite direction to the first conveying screw 46a. In this way, the developer is circulated between the developing chamber 45a and the stirring chamber 45b through the openings (i.e., communication parts) formed at both ends of the partition wall 44 by the conveyance caused by the rotation of the first and second conveying screws 46a and 46b. In this embodiment, the developing chamber 45a and the stirring chamber 45b are disposed in a substantially horizontal direction, but the developing chamber 45a and the stirring chamber 45b may be disposed, for example, substantially vertically up and down, or may be disposed in a positional relationship between the horizontal direction and the vertical direction.

[0031] In this embodiment, an opening is provided at a position corresponding to the development area G facing the photosensitive drum 1 of the developer container 42, and the developing sleeve 41 is rotatably arranged at a predetermined interval between the photosensitive drum 1 and the developing sleeve 41 so that a part of the developing sleeve 41 is exposed from the opening toward the photosensitive drum 1. The developing device 4 develops the developer on the developing sleeve 41 transported to the development area G in a state where the developer is in contact with the photosensitive drum 1. The developing sleeve 41 is made of a non-magnetic material such as aluminum or stainless steel, and a magnet roller 47, which is a magnetic field generating means, is arranged inside the developing sleeve 41 so as not to rotate. The developing sleeve 41 is driven to rotate in the direction of the arrow R3 in FIG. 4 (counterclockwise direction), and carries a two-component developer whose layer thickness is regulated by the cutting of the magnetic brush by the cutting member 43. The developing sleeve 41 transports the developer whose layer thickness is regulated to the development area G facing the photosensitive drum 1, and supplies toner to the electrostatic latent image formed on the photosensitive drum 1 to develop the electrostatic latent image. At this time, in order to improve the development efficiency, that is, the rate at which the toner is applied to the electrostatic latent image, a development voltage (development bias) in the form of a superimposed DC voltage and AC voltage is applied to the development sleeve 41 from a development power source (not shown). The brush cut-off member 43 is composed of a non-magnetic member (regulation blade) made of plate-like aluminum or the like extending along the rotation axis direction of the development sleeve 41. The brush cut-off member 43 is also disposed upstream of the photosensitive drum 1 in the rotation direction of the development sleeve 41. The developer (toner and carrier) passes between the tip of the brush cut-off member 43 and the development sleeve 41 and is sent to the development area G. In this embodiment, in the development area G, the development sleeve 41 rotates so that the moving direction of its surface is the same as the moving direction of the surface of the photosensitive drum 1. The peripheral speed of the development sleeve 41 can be made faster than the peripheral speed of the photosensitive drum 1.

[0032] A hopper 17, which is a replenishing device serving as a replenishing means, is disposed on the upper portion of the developing device 4. The hopper 17 accommodates a replenishing developer (toner, or a replenishing two-component developer in which toner and carrier are mixed) supplied from a toner bottle 16 serving as a replenishing container. The hopper 17 is provided with a replenishing screw 18 serving as a replenishing member at its lower portion, and one end of the replenishing screw 18 extends to the position of a replenishing port 48 provided at one end in the longitudinal direction (substantially parallel to the rotation axis direction of the photosensitive drum 1) of the developing device 4. The toner consumed by image formation is replenished from the hopper 17 through the replenishing port 48 to the developing container 42 by the conveying force due to the rotation of the replenishing screw 18 and the gravity acting on the replenishing developer. In this embodiment, the replenishing amount of the replenishing developer is set by the number of rotations of the replenishing screw 17. This number of rotations is set by a control unit 200 (FIG. 4) described later based on a video count value of image data described later, etc.

[0033] 3. Developer Next, the developer in this embodiment will be further described. As described above, in this embodiment, the developing device 4 develops the electrostatic latent image on the photosensitive drum 1 using a two-component developer in which a carrier (magnetic carrier particles) and a toner (non-magnetic toner particles) are mixed as the developer. In this embodiment, a developer in which the carrier and the toner are mixed to a weight ratio of 91:9 (toner concentration: 9%) is used. In this embodiment, the total weight of the initial developer contained in the developing device 4 is 208 g.

[0034] In this embodiment, ferrite particles coated with silicone resin were used as the carrier. This carrier has a saturation magnetization of 24 [Am] with respect to an applied magnetic field of 240 [kA / m]. 2 / kg]. In addition, the specific resistance of this carrier at an electric field strength of 3000 [V / cm] is 1×10 7 [Ω cm]~1×10 8 [Ω·cm], and the weight average particle size is 50 μm.

[0035] The toner is composed of at least a binder resin, a colorant, and a charge control agent. In this embodiment, a styrene-acrylic resin is used as the binder resin. However, the binder resin is not limited to this, and styrene-based, polyester-based, polyethylene-based, and other resins can also be used. As the colorant, various pigments and various dyes are used. The colorant may be used alone or in combination with a plurality of types. The charge control agent may contain a charge control agent for reinforcement as necessary. As the charge control agent for reinforcement, a nigrosine dye, a triphenylmethane dye, or the like can be used.

[0036] The toner contains wax. The wax is contained to improve the fixability and releasability from the fixing member (fixing roller 10a) during fixing. As the wax, paraffin wax, carnauba wax, polyolefin, etc. can be used, and they are used by kneading and dispersing in a binder resin. In this embodiment, the toner used is a resin in which a binder, a colorant, a charge control agent, and wax are kneaded and dispersed, and the resin is pulverized by a mechanical pulverizer. The melting point of the wax used in this embodiment is 100°C or less.

[0037] In addition, an external additive is added to the toner. Examples of the external additive include amorphous silica that has been subjected to a hydrophobic treatment, or inorganic oxide particles such as titanium oxide and titanium compounds. These external additive particles are added to the toner base (base particles) to adjust the powder fluidity and charge amount of the toner. The average particle size of the external additive particles is preferably 1 nm or more and 100 nm or less. In this embodiment, titanium oxide with an average particle size of 50 nm is added to the toner base at a weight ratio of 0.5 wt%, and amorphous silica with average particle sizes of 2 nm and 100 nm is added to the toner base at a weight ratio of 0.5 wt% and 1.0 wt%, respectively.

[0038] The toner in this embodiment having the above-mentioned structure had a weight average particle size of 6.6 μm when the particle size was measured using a powder particle size image analyzer FPIA-3000 manufactured by Sysmex Corporation.

[0039] 4.Belt cleaning device Next, the belt cleaning device 8 in this embodiment will be further described. Fig. 3 is a schematic cross-sectional view (a cross-section substantially perpendicular to the rotation axis direction of the photosensitive drum 1 and the support roller of the intermediate transfer belt 7) of the belt cleaning device 8 in this embodiment.

[0040] The belt cleaning device 8 has a cleaning container (casing) 81 having an opening 81a on the intermediate transfer belt 7 side. A cleaning blade (here, simply referred to as "blade") 82 as a cleaning member is disposed at the opening 81a of the cleaning container 81. The blade 82 is configured as a plate-like member of a predetermined thickness having a predetermined length in the longitudinal direction and a short side direction approximately perpendicular to the longitudinal direction, which are disposed (approximately parallel in this embodiment) along a direction (width direction) approximately perpendicular to the moving direction of the surface of the intermediate transfer belt 7. In this embodiment, the blade 82 is formed of urethane rubber as an elastic material. The longitudinal length of the blade 82 is set to a length that is approximately the same as or wider than the length of the image forming area (area where a toner image can be formed) on the intermediate transfer belt 7 in the direction approximately perpendicular to the moving direction of the surface of the intermediate transfer belt 7.

[0041] The blade 82 has one end (fixed end) in the short side direction fixed to the support member 83. The support member 83 is attached to the cleaning container 81 so as to be rotatable (swingable) about a rotation axis that is substantially parallel to a direction substantially perpendicular to the moving direction of the surface of the intermediate transfer belt 7. In this manner, the blade 82 is attached to the cleaning container 81 via the support member 83 so as to be rotatable (swingable). The blade 82 has an edge portion 82a on the outer side of the cleaning container 81 at the tip of the other end (free end) side in the short side direction, which is in contact with the surface of the intermediate transfer belt 7 at the portion wound around the tension roller 74. The support member 83 is biased by a pressure spring 86, which is a biasing member serving as a biasing means, in a direction in which the blade 82 rotates so as to press the edge portion 82a of the blade 82 against the surface of the intermediate transfer belt 7. The blade 82 is in contact with the surface of the intermediate transfer belt 7 so as to be in a counter direction to the moving direction of the surface of the intermediate transfer belt 7. That is, the blade 82 is in contact with the surface of the intermediate transfer belt 7 with the tip on the free end side facing upstream in the moving direction of the surface of the intermediate transfer belt 7 during image formation. The contact portion (nip portion) between the blade 82 (edge ​​portion 82a) and the intermediate transfer belt 7 is a blade nip portion (cleaning portion, cleaning nip portion) Q.

[0042] In addition, at the opening 81 of the cleaning container 81, a scooping sheet 84 is attached as a contact member upstream of the blade 82 in the moving direction of the surface of the intermediate transfer belt 7. The scooping sheet 84 is configured of a sheet-like member of a predetermined thickness having a predetermined length in the longitudinal direction and a lateral direction approximately perpendicular to the longitudinal direction, which are arranged along a direction (approximately parallel in this embodiment) approximately perpendicular to the moving direction of the surface of the intermediate transfer belt 7. In this embodiment, the scooping sheet 84 is formed of a flexible plastic sheet. One end of the scooping sheet 84 in the lateral direction is fixed to and supported by the cleaning container 81. The tip of the scooping sheet 84 on the free end side in the lateral direction is in contact with the intermediate transfer belt 7. The tip of the scooping sheet 84 on the free end side is in contact with the intermediate transfer belt 7 so as to face the downstream side of the moving direction of the surface of the intermediate transfer belt 7 during image formation. The scoop sheet 84 allows the toner scraped off by the blade 82 to fall into the cleaning container 81, and also prevents the toner from flowing back toward the intermediate transfer belt 7.

[0043] In addition, a collected toner transport screw 85 is disposed in the cleaning container 81 as a collected toner transport member. The collected toner transport screw 85 transports the toner collected in the cleaning container 81 by the blade 82 in the longitudinal direction of the cleaning container 81 (substantially parallel to a direction substantially perpendicular to the moving direction of the surface of the intermediate transfer belt 7). Then, the collected toner is discharged from a discharge port (not shown) provided in the cleaning container 81 to the outside of the cleaning container 81. The toner discharged from the cleaning container 81 is transported to a collected toner box (not shown) provided in the image forming apparatus 100 through a transport path (not shown) provided in the image forming apparatus 100.

[0044] 5. Control Mode 4 is a schematic block diagram showing the control mode of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 is provided with a control unit 200 as a control means. The control unit 200 is configured to have a CPU as an arithmetic processing means which is a central element for performing arithmetic processing, a ROM, RAM and non-volatile memory as storage means (storage medium), an input / output circuit as an input / output means, and the like. The ROM stores a control program, a data table obtained in advance, and the like. The RAM stores information input to the control unit 200, detected information, arithmetic results, and the like. The input / output circuit inputs and outputs signals between the control unit 200 and devices connected thereto.

[0045] The control unit 200 is connected to each part of the image forming apparatus 100, such as the image forming unit P including the exposure device 3. The control unit 200 controls each part of the image forming apparatus 100 to execute a job (image forming job) based on a signal (start signal, image signal) input from an external device (not shown) such as a personal computer (information processing device) in response to an operation by a user (operator). Note that a job is a series of operations that form and output an image on one or more recording materials S, which is started by one start signal. The control unit 200 is also provided with a sheet number counter 201 as a sheet number counting means that counts (stores) the number of sheets on which images are formed. The control unit 200 is also provided with a drive time counter 202 as a drive time counting means that counts (stores) the drive time of the developing device 4 (the rotation time of the developing sleeve 41). In this embodiment, the sheet number counter 201 and the drive time counter 202 are realized by a CPU and a non-volatile memory.

[0046] The control unit 200 is also connected to an image processing unit (video controller) 300 that generates image data used for image formation in the image forming apparatus 100 based on a signal input from an external device. Color image data is input from an external device to the image processing unit 300 as RGB image data. The image processing unit 300 converts the luminance data of the input RGB image data into CMY density data (CMY image data) based on a lookup table (LUT) in a LOG conversion unit. The image processing unit 300 also extracts black (K) component data from the CMY image data in a masking / UCR unit, and performs matrix calculation on the CMYK image data to correct color turbidity of the recording color material. The image processing unit 300 also performs density correction for each color of the input CMYK image data in a lookup table unit (LUT unit) using a gamma lookup table (γ lookup table) for matching the image data to the ideal gradation characteristics of the image forming apparatus 100. In addition, the image processing unit 300 outputs a pulse signal having a pulse width corresponding to the level of the image data (image signal) input from the LUT unit in the pulse width modulation unit. Based on this pulse signal, the laser driver in the exposure device 3 drives the laser light emitting element, and the photosensitive drum 1 is irradiated with laser light to form an electrostatic latent image. In addition, the image processing unit 300 is provided with a video count unit 301 as a developer consumption information acquisition unit (video count unit). The video count unit 301 accumulates the level (0 to 255 level) of each pixel at 600 dpi of the image data input to the LUT unit for one surface of the image. This image data accumulation value is called a video count value. This video count value is a maximum value of 1023 when the entire surface of the output image is at 255 level. It is also possible to obtain the video count value by similarly calculating the image signal from the laser driver using a laser signal count unit instead of the video count unit 301.

[0047] 6. Toner band formation operation Next, the toner band forming operation in this embodiment will be described. In this embodiment, the image forming apparatus 100 executes an operation of forming a lubricating toner band that functions as a lubricant in order to suppress the occurrence of abnormal noises such as chattering and squealing and turning over of the blade 82 due to poor slip between the blade 82 and the intermediate transfer belt 7. In addition, in this embodiment, the image forming apparatus 100 executes an operation of forming a discharged toner band for discharging deteriorated toner in the developing device 4 when a low-printing rate image with a low printing rate is continuously formed. Note that the printing rate is the ratio of the area of ​​the printed portion (image portion, portion on which the toner is placed) in the image forming area, and is 100% when the entire image forming area is a solid image, and is 0% when there is no printed portion and a solid white image. In this embodiment, the toner band (lubricating toner band, discharged toner band) is formed by the same process (charging, exposure, development) as the normal image formation described above.

[0048] As a control method for determining whether or not a toner band (lubricating toner band, spit toner band) is required to be formed, any available method such as a known method can be used as appropriate. Here, an example of control for determining whether or not a toner band (lubricating toner band, spit toner band) is required to be formed will be briefly described. In this embodiment, a case will be described in which the toner band (lubricating toner band, spit toner band) formed on the photosensitive drum 1 is transferred to the intermediate transfer belt 7 and conveyed to the belt cleaning device 8 without being transferred to the recording material S.

[0049] 6-1. Lubricating toner band formation operation First, the operation of forming the lubricating toner zone will be described. In this embodiment, the image forming apparatus 100 executes the operation of forming the lubricating toner zone for each predetermined number of images formed. Fig. 5 is a flow chart of the control for determining whether or not the operation of forming the lubricating toner zone is necessary in this embodiment. In this embodiment, the lubricating toner zone is formed in the image forming unit PK for K color.

[0050] When a job start signal is input, the control unit 200 acquires a count value of the number of images formed from the sheet counter 201, which is related to the control of the formation operation of the lubricating toner zone (S101). Next, the control unit 200 judges whether the number of images formed is equal to or greater than a predetermined threshold (for example, 100 sheets) (S102). When the control unit 200 judges in S102 that the number of images formed is equal to or greater than the threshold, the control unit 200 forms a lubricating toner zone in a non-image forming area (area other than the image forming area) on the photosensitive drum 1. Then, the control unit 200 transfers the lubricating toner zone to the intermediate transfer belt 7, passes the secondary transfer portion T2, and supplies the lubricating toner zone to the edge portion 82a of the blade 82 of the belt cleaning device 8 (S103). In order to pass the secondary transfer portion T2, the secondary transfer roller 9 can be separated from the intermediate transfer belt 7, or a voltage of the same polarity as the normal charging polarity of the toner can be applied to the secondary transfer roller 9. This also applies to the formation operation of the discharged toner zone, which will be described later. When the lubricating toner zone is formed, the control unit 200 resets the count value of the number of image formation sheets related to the control of the lubricating toner zone formation operation to an initial value (zero in this embodiment) (S104). After that, the control unit 200 performs image formation (S105). The control unit 200 also determines whether or not all image formation of the job has been completed (S106), and if not, returns to the process of S101, and if completed, ends the job.

[0051] Moreover, when the control unit 200 determines in S102 that the number of images formed is not equal to or greater than the threshold (is less than the threshold), the control unit 200 proceeds to the process of S105 without forming the lubricating toner band.

[0052] The lubricating toner band may be formed at any time other than during image formation when an image is transferred to the recording material S and output. Examples of non-image formation times include pre-rotation time, which is a preparatory operation period before the image formation of a job, a paper interval time, which is a period corresponding to the period between image formations of a job, and post-rotation time, which is a tidying operation (preparatory operation) period after the image formation of a job. This also applies to the formation operation of the spit toner band, which will be described later.

[0053] Also, the lubricating toner band may be formed based on the result of judging the level of lubrication between the blade 82 and the intermediate transfer belt 7. For example, as described above, when it is necessary to slow down the conveying speed of the recording material S, the slip between the blade 82 and the intermediate transfer belt 7 may become poor if the rotation speed of the intermediate transfer belt 7 is slowed down. That is, when thick paper or OHT (Over Head Transparency) is used as the recording material S, the conveying speed of the recording material S when fixing the toner image may be slower than that of normal printing paper (plain paper). This is because thick paper has a large heat capacity and therefore takes a long time to fix. Also, OHT is because it is necessary to melt the toner sufficiently so that it is distributed smoothly on the OHT. If the toner is not sufficiently smooth, light may be scattered when projected by a projector, and beautiful color reproduction may not be possible. However, in recent years, as the image forming apparatus has become smaller, it has become difficult to secure a sufficient space between the secondary transfer position and the fixing device. When the distance between the secondary transfer position and the fixing device is shorter than the length of the recording material S in the transport direction, the fixing operation is performed at the leading end of the recording material S, and at the same time, the secondary transfer is performed at the trailing end of the recording material S. For this reason, when the recording material S is an OHT or thick paper that requires a slow transport speed during fixing, the rotation speed of the intermediate transfer belt 7 must also be slowed down. When the rotation speed of the intermediate transfer belt 7 is slowed down in accordance with the type of recording material S in this way, a lubricating toner band may be formed at a predetermined timing.

[0054] The pattern of the lubricating toner band will be described in detail later.

[0055] 6-2. Formation of discharged toner band Next, the operation of forming the spit toner band will be described. In this embodiment, the image forming apparatus 100 judges whether or not the operation of forming the spit toner band is necessary for each predetermined number of images formed, based on the driving time of the developing device 4 (the rotation time of the developing sleeve 41) and the video count value, and executes the operation of forming the spit toner band as necessary. Fig. 6 is a flow chart of the control for judging whether or not the operation of forming the spit toner band is necessary in this embodiment. Note that, here, the explanation will be given focusing on one image forming portion P as a representative, but the same control is performed for each image forming portion P.

[0056] When a job start signal is input, the control unit 200 acquires a count value of the number of images formed, which is related to the control of the formation operation of the discharged toner band, from the sheet number counter 201 (S201). Next, the control unit 200 judges whether the number of images formed is equal to or greater than a predetermined threshold (for example, 100 sheets) (S202). When the control unit 200 judges in S202 that the number of images formed is equal to or greater than the threshold, it acquires an integrated drive time St from the drive time counter 202 and an integrated video count value Vall from the video count unit 301 (S203). Here, the integrated drive time St is an integrated value of the drive time (rotation time of the developing sleeve 41) of the developing device 4 for each predetermined number of images formed (threshold) (it may also include the drive time of the developing device 4 during the paper interval, pre-rotation, etc.). Moreover, the integrated video count value Vall is an integrated value of the video count value for each color for each predetermined number of images formed (threshold). The video count value may include a video count value due to the formation of a control image (such as density control, toner supply control, and color shift control) in addition to a video count value due to the image formation of a normal document. Next, the control unit 200 calculates an index value Vall / St of the toner consumption amount per unit drive time based on the integrated drive time St and the integrated video count value Vall (S204). This index value Vall / St correlates with the average print rate for each predetermined number of image formations (threshold), that is, the degree of deterioration of the toner in the developing device 4. Next, the control unit 200 judges whether the index value Vall / St is less than a predetermined threshold (S205). If the control unit 200 judges in S205 that the index value Vall / St is less than the threshold, it ejects toner into a non-image formation area (area outside the image formation area) on the photosensitive drum 1 to form a toner band. Then, this discharged toner band is transferred onto the intermediate transfer belt 7, passed through the secondary transfer portion T2, and supplied to the edge portion 82a of the blade 82 of the belt cleaning device 8 (S206). In this case, the amount of toner consumed per unit driving time is small, and it can be determined that the toner in the developing device 4 is deteriorating. Here, the threshold value of the index value Vall / St can be preset as the index value Vall / St at which problems due to degraded toner (such as toner scattering and fogging) may occur.Next, the control unit 200 resets the accumulated drive time St, the accumulated video count value Vall, and the count value of the number of image formation sheets related to the control of the formation operation of the discharged toner band to their initial values ​​(zero in this embodiment) (S207). After that, the control unit 200 performs image formation (S208). In addition, the control unit 200 determines whether or not all image formation of the job has been completed (S209), and if not, returns to the process of S201, and if completed, ends the job.

[0057] Furthermore, if the control unit 200 determines in S205 that the index value Vall / St is not less than the threshold (is equal to or greater than the threshold), it proceeds to the process of S207 without forming a discharged toner band. In this case, it is determined that the amount of toner consumed per unit driving time is sufficiently large and the deterioration of the toner in the developing device 4 is not progressing. The subsequent operations are the same as those described above.

[0058] Furthermore, when the control unit 200 determines in S202 that the number of sheets on which images have been formed is not equal to or greater than the threshold (is less than the threshold), the control unit 200 skips the processes from S203 to S207 and proceeds to the process of S208. The subsequent operations are the same as those described above.

[0059] Here, an example of control for determining whether or not the discharged toner band forming operation is required based on the driving time of the developing device 4 (the rotation time of the developing sleeve 41) and the video count value has been described, but the present invention is not limited to this. For example, as described in Patent Document 2, control for determining whether or not the discharged toner band forming operation is required may be performed as follows. That is, for each image formation, when the index value (video count value) of the toner consumption amount is smaller than a predetermined threshold value, the difference between the threshold value and the index value is calculated. Then, when the integrated value obtained by accumulating the calculated difference reaches a predetermined value, the discharged toner band is formed. Also, for example, the average printing rate for a predetermined period (for each predetermined number of image formation sheets, etc.) may be calculated based on image data, and the discharged toner band forming operation may be performed when the calculated average printing rate is less than a predetermined threshold value. Even with such control, the discharged toner band can be formed according to the degree of deterioration of the toner in the developing device 4 due to the printing rate of the image to be formed.

[0060] The pattern of the ejected toner band will be described in detail later.

[0061] 7. Toner band cleaning failure Next, the cleaning failure of the toner zone (lubricating toner zone, spit toner zone) will be described. FIG. 7 is a schematic diagram showing an enlarged view of the vicinity of the blade nip portion Q, which is the contact portion between the blade 82 (edge ​​portion 82a) and the intermediate transfer belt 7. In relation to the belt cleaning device 8, upstream and downstream mean upstream and downstream in the moving direction of the surface of the intermediate transfer belt 7, even if not specifically stated. Here, the moving direction of the surface of the intermediate transfer belt 7 is also called the "conveying direction", and the direction (width direction) approximately perpendicular to the moving direction of the surface of the intermediate transfer belt 7 is also called the "longitudinal direction". The longitudinal direction corresponds to the main scanning direction of the exposure device 3 (approximately parallel to the rotation axis direction of the photosensitive drum 1), and the conveying direction corresponds to the sub-scanning direction of the exposure device 3 (approximately parallel to the moving direction of the surface of the photosensitive drum 1).

[0062] A force is applied to the blade 82 so that the tip of the free end side of the blade 82 (here, simply referred to as the "tip") contacts the intermediate transfer belt 7. As a result, the residual toner and toner band on the intermediate transfer belt 7 are blocked by the blade 82, and the intermediate transfer belt 7 is cleaned. Near the upstream side of the blade nip Q, there is an "external additive blocking layer" formed by blocking the external additive released from the toner by the blade 82. Furthermore, on the upstream side of the external additive blocking layer, there is a "toner non-moving layer" formed by blocking the residual toner and toner band. Furthermore, on the upstream side of the toner non-moving layer, there is a "toner deceleration layer" formed by the transfer residual toner and toner band toner adhering to the intermediate transfer belt 7 and moving from the upstream side to the downstream side colliding with the toner non-moving layer and the moving speed being decelerated. The toner deceleration layer and the toner non-moving layer are collectively called the "toner retention layer."

[0063] When a toner band (lubricating toner band, spit toner band) is formed on the intermediate transfer belt 7, the toner in the toner band is pushed into the toner accumulation layer. The force of the toner in the toner band being pushed into the toner accumulation layer generates a force pushing up the blade 82. When the force pushing up the blade 82 becomes larger than the force pressing the tip of the blade 82 against the intermediate transfer belt 7, the toner in the toner accumulation layer and the toner in the toner band push up the blade 82 and slip through the blade 82, causing a cleaning failure of the toner band. As described above, the toner band (lubricating toner band, spit toner band) is generally formed over almost the entire image forming area in the longitudinal direction that is approximately perpendicular to the conveying direction of the intermediate transfer belt 7 (here, simply referred to as the "entire longitudinal area"). When the toner band is present over the entire longitudinal area, the toner in the toner band pushes up the blade 82 over the entire longitudinal area, which is likely to cause a cleaning failure of the toner band.

[0064] Here, the distortion of the blade 82 caused by the toner band (lubricating toner band, spit toner band) will be described. FIG. 8 is a graph showing an example of the result of measuring the distortion of the blade 82 using a strain gauge when the toner band is formed on the intermediate transfer belt 7 and supplied to the edge portion 82a of the blade 82. The toner band (lubricating toner band, spit toner band) used had a horizontal 4 line-1 space pattern repeatedly formed in the conveying direction over the entire length. The horizontal 4 line-1 space pattern was repeatedly formed over 2 mm in the conveying direction for the lubricating toner band and 210 mm in the conveying direction for the spit toner band. The horizontal 4 line-1 space is a pattern consisting of a 4 dot printed portion (image portion) in the conveying direction and a 1 dot non-printed portion (non-image portion) in the conveying direction adjacent to the printed portion. 8, it can be seen that, at the timing when the toner band reaches the blade nip portion Q, the blade 82 is distorted in the direction opposite to the direction in which the blade 82 is pressed toward the intermediate transfer belt 7 (also referred to here as the "no-load direction") This is the same for both the lubricating toner band and the spit toner band.

[0065] 8, when the process speed (image forming speed) is 200 mm / sec, the time it takes for the blade 82 to distort in the no-load direction is about 10 msec, which corresponds to a distance of about 2 mm in the transport direction. Since the lubricating toner band is formed over an area of ​​2 mm in the transport direction, this means that the blade 82 distorts in the no-load direction over the entire area of ​​the lubricating toner band in the transport direction, and poor cleaning occurs over the entire area of ​​the lubricating toner band in the transport direction.

[0066] In addition, the discharged toner band is formed over 210 mm in the transport direction, but the distortion of the blade 82 in the unloaded direction occurs at about 2 mm of the leading end of the discharged toner band in the transport direction. Therefore, the distance in the transport direction where the cleaning failure occurs is also about 2 mm of the leading end of the discharged toner band in the transport direction. This is considered to be due to the following reason. That is, the discharged toner band is pushed into the toner accumulation layer as shown in FIG. 7, so that the leading end of the discharged toner band in the transport direction has the greatest force pushing up the blade 82. As a result, the toner in the toner accumulation layer and the toner at the leading end of the discharged toner band in the transport direction slip through the blade 82, causing a cleaning failure of about 2 mm in the transport direction. Then, since the toner in the toner accumulation layer disappears by slipping through the blade 82, the force pushing up the blade 82 decreases, and the blade 82 is pressed toward the intermediate transfer belt 7. Therefore, even if the discharged toner band is formed over 210 mm in the transport direction, the distortion of the blade 82 in the unloaded direction occurs only at about 2 mm of the leading end in the transport direction, causing a cleaning failure of about 2 mm in the transport direction.

[0067] In the configuration of this embodiment, cleaning defects are likely to occur at about 2 mm from the leading edge of the toner band, and this range may vary depending on the setting conditions of the blade 82 (contact pressure, etc.), the amount of toner in the toner band, the fluidity of the toner (type of toner), etc. However, it can be seen that cleaning defects tend to occur more easily within a certain range at the leading edge of the toner band than on the trailing edge side of that range.

[0068] 8. Toner belt in this embodiment Next, the toner bands (lubricating toner band, spit toner band) in this embodiment will be described. In this embodiment, in order to suppress poor cleaning of the toner bands (lubricating toner band, spit toner band) as described above, the formation operation of the toner bands (lubricating toner band, spit toner band) is controlled, and more specifically, the pattern of the toner bands (lubricating toner band, spit toner band) is controlled.

[0069] First, the lubricating toner band will be described with reference to FIG. 9. FIG. 9(a) is a schematic diagram for explaining the pattern of the lubricating toner band of Comparative Example 1. The lubricating toner band of Comparative Example 1 is an example of a conventional lubricating toner band. The lubricating toner band of Comparative Example 1 is formed by repeatedly forming a pattern (solid line frame in FIG. 9(a)) of horizontal 4 Line-1 Space ("Horizontal 4L1S"), which is a minimum unit pattern, over 2 mm in the conveying direction and over the entire longitudinal area (305 mm in the longitudinal direction). As described above, the horizontal 4 Line-1 Space is a pattern consisting of a 4-dot printed part in the conveying direction and a 1-dot non-printed part in the conveying direction adjacent to the printed part. It takes 0.01 sec to form the lubricating toner band of Comparative Example 1 when the process speed is 200 mm / sec. Then, in the lubricating toner band of Comparative Example 1, cleaning failure of the lubricating toner band occurs due to the mechanism described with reference to FIG. 7 and FIG. 8. Here, the cleaning failure of the toner band was evaluated as follows. A toner band is formed, and after one revolution of the intermediate transfer belt 7, a secondary transfer process is performed by passing the recording material S through the secondary transfer section T2 so that it overlaps with the toner band, and the recording material S passes through the fixing device 10 and is then output from the image forming apparatus 100. The presence or absence of the toner band on the recording material S is then visually confirmed, and if there is a toner band, it is determined that a cleaning failure of the toner band has occurred, and if there is no toner band, it is determined that a cleaning failure of the toner band has not occurred. Furthermore, the toner concentration (here, also referred to as "slip-through toner concentration") at the location on the recording material S corresponding to the toner band is measured using a reflection densitometer. This is similar to the other examples described later.

[0070] On the other hand, FIG. 9(b) is a schematic diagram for explaining the pattern of the lubricating toner band of this embodiment. In the lubricating toner band of this embodiment, the minimum unit pattern (solid line frame in FIG. 9(b)) is set to 1 Line-8 Space ("1 L 8 S"). That is, the lubricating toner band of this embodiment is formed by repeatedly forming a pattern of 8 Line-1 Space, which is the minimum unit pattern, over 14 mm in the conveying direction, over the entire longitudinal area (305 mm in the longitudinal direction). Note that 1 Line-8 Space is a pattern consisting of a printed part of 1 dot in the conveying direction and a non-printed part of 8 dots in the conveying direction adjacent to the printed part. It takes 0.07 sec to form the lubricating toner band of this embodiment when the process speed is 200 mm / sec. In the lubricating toner band of this embodiment, the amount of toner supplied per unit time to the edge part 82a of the blade 82 is less than that in the lubricating toner band of Comparative Example 1. As a result, the force pushing up the blade 82 by the lubricating toner band becomes smaller than the force pressing the tip of the blade 82 against the intermediate transfer belt 7, making it possible to suppress poor cleaning of the lubricating toner band. However, in the lubricating toner band of this embodiment, in order to supply the same amount of toner to the edge portion 82a of the blade 82 as in the lubricating toner band of Comparative Example 1, it is necessary to form a horizontal 1 Line-8 Space pattern over 14 mm in the transport direction.

[0071] Here, the lubricating toner band of this embodiment, for example, per unit area of ​​1 mm in the transport direction × 1 mm in the longitudinal direction, is as follows: That is, the lubricating toner band of this embodiment is a pattern of 1 horizontal line and 8 spaces, which is the minimum unit pattern, repeated over 14 mm in the transport direction and the entire longitudinal area (range of 305 mm in the longitudinal direction). In this case, for example, per unit area of ​​1 mm in the transport direction × 1 mm in the longitudinal direction, the 1 horizontal line portion (dashed line frame in FIG. 9(b)), which is the printed portion (maximum density portion), has a relationship (aspect ratio) between the length along the transport direction (vertical length W1) and the length along the longitudinal direction (horizontal length W2), such that vertical length W1<horizontal length W2.

[0072] Table 1 shows the minimum unit pattern, length in the transport direction, occurrence of cleaning failure, slip-through toner concentration, and productivity (toner band forming operation time) in the lubricating toner bands of the above-mentioned Comparative Example 1 and this embodiment.

[0073] [Table 1]

[0074] Next, the discharged toner band will be described with reference to FIG. 10. FIG. 10(a) is a schematic diagram for explaining the pattern of the discharged toner band of Comparative Example 2. The discharged toner band of Comparative Example 2 is an example of a conventional discharged toner band. The minimum unit pattern of the discharged toner band of Comparative Example 2 is the same as the minimum unit pattern of the lubricating toner band of Comparative Example 1. That is, the discharged toner band of Comparative Example 2 is formed by repeatedly forming a minimum unit pattern of horizontal 4 Line-1 Space ("horizontal 4L1S") (solid line frame in FIG. 10(a)) over 210 mm in the conveying direction and over the entire longitudinal area (305 mm range in the longitudinal direction). It takes 1.05 sec to form the discharged toner band of Comparative Example 2 when the process speed is 200 mm / sec. In the discharged toner band of Comparative Example 2, cleaning failure of the discharged toner band occurs due to the mechanism described with reference to FIG. 7 and FIG. 8. Moreover, in the discharged toner band of Comparative Example 2, a length of 210 mm in the transport direction is required to discharge the required amount of deteriorated toner in the developing device 4. Therefore, to form the discharged toner band of Comparative Example 2, 1.05 sec is required when the process speed is 200 mm / sec.

[0075] Next, FIG. 10(b) is a schematic diagram for explaining the pattern of the discharged toner band of Comparative Example 3. In Comparative Example 3, the minimum unit pattern is the same as the minimum unit pattern of the lubricating toner band of the present embodiment described above in order to suppress cleaning failure, in comparison with Comparative Example 2. In the discharged toner band of Comparative Example 3, the minimum unit pattern (solid line frame in FIG. 10(b)) is set to 1 Line-8 Space ("1 L 8 S"). That is, the discharged toner band of Comparative Example 3 is formed by repeatedly forming a minimum unit pattern of 8 Line-1 Space in the horizontal direction over 1470 mm in the conveying direction and over the entire longitudinal area (305 mm in the longitudinal direction). It takes 7.35 sec to form the discharged toner band of Comparative Example 3 when the process speed is 200 mm / sec. In the discharged toner band of Comparative Example 3, the amount of toner supplied per unit time to the edge portion 82a of the blade 82 is less than that in the discharged toner band of Comparative Example 2. As a result, the force pushing up the blade 82 by the discharged toner band becomes smaller than the force pressing the tip of the blade 82 against the intermediate transfer belt 7, and poor cleaning of the discharged toner band can be suppressed. However, in the discharged toner band of Comparative Example 3, in order to discharge the required amount of deteriorated toner in the developing device 4 in a horizontal 1 Line-8 Space pattern, a length of 1470 mm in the transport direction is required (7 times that of Comparative Example 2). Therefore, in order to form the discharged toner band of Comparative Example 3, 7.35 sec is required when the process speed is 200 mm / sec. In other words, compared to 1.05 sec in Comparative Example 3, this is an increase of 6.30 sec, so that there is a possibility that productivity will decrease if, for example, a low print rate image with a low print rate is continuously formed.

[0076] On the other hand, FIG. 10(c) is a schematic diagram for explaining the pattern of the discharged toner band of this embodiment. In the discharged toner band of this embodiment, the minimum unit pattern (solid line frame in FIG. 10(c)) is vertical 2Line-5Space ("vertical 2L5S"). That is, the discharged toner band of this embodiment is formed by repeatedly forming a pattern of vertical 2Line-5Space, which is the minimum unit pattern, over 420 mm in the conveying direction, over the entire longitudinal area (range of 305 mm in the longitudinal direction). Note that vertical 2Line-5Space is a pattern consisting of a printed part of 2 dots in the longitudinal direction and a non-printed part of 5 dots in the longitudinal direction adjacent to the printed part. It takes 2.10 seconds to form the discharged toner band of this embodiment when the process speed is 200 mm / sec. In the discharged toner band of this embodiment, the amount of toner supplied per unit time to the edge part 82a of the blade 82 is less than that in the discharged toner band of Comparative Example 2. As a result, the force pushing up the blade 82 by the discharged toner band becomes smaller than the force pressing the tip of the blade 82 against the intermediate transfer belt 7, and cleaning failure of the discharged toner band can be suppressed. In addition, in the discharged toner band of this embodiment, in order to discharge the required amount of deteriorated toner in the developing device 4 in a vertical 2 Line-5 Space pattern, a length of 420 mm in the conveying direction is required (twice that of Comparative Example 2). Therefore, when the process speed is 200 mm / sec, 2.10 sec is required to form the discharged toner band of this embodiment. However, this is a reduction of 5.25 sec compared to 7.35 sec in Comparative Example 3. In this way, according to the discharged toner band of this embodiment, it is possible to suppress the cleaning failure of the discharged toner band while suppressing the decrease in productivity.

[0077] Here, the discharged toner band of this embodiment is as follows, for example, when viewed per unit area of ​​1 mm in the transport direction × 1 mm in the longitudinal direction. In other words, the discharged toner band of this embodiment is a pattern of 2 vertical lines and 5 spaces, which is the minimum unit pattern, repeated over the entire longitudinal area (range of 305 mm in the longitudinal direction) over 420 mm in the transport direction. In this case, when viewed per unit area of ​​1 mm in the transport direction × 1 mm in the longitudinal direction, for example, the relationship (aspect ratio) between the length in the transport direction (vertical length W1) and the length in the longitudinal direction (horizontal length W2) of the printed portion (maximum density portion) of the vertical 2-line portion (dashed line frame portion in FIG. 10(c)) is vertical length W1>horizontal length W2.

[0078] In other words, in this embodiment, the aspect ratio (vertical length W1<horizontal length W2) of the printed portion (1 horizontal line portion) when the lubricating toner band is viewed per unit area of ​​1 mm in the transport direction × 1 mm in the longitudinal direction is different from the aspect ratio (vertical length W1>horizontal length W2) of the printed portion (2 vertical lines portion) when the ejected toner band is viewed per unit area of ​​1 mm in the transport direction × 1 mm in the longitudinal direction.

[0079] Table 2 summarizes the minimum unit pattern, length in the transport direction, whether or not cleaning failure occurred, the concentration of passed-through toner, and productivity (toner band formation operation time) for the ejected toner bands of the above-mentioned Comparative Example 2, Comparative Example 3, and this embodiment.

[0080] [Table 2]

[0081] Here, the reason for making the pattern of the lubricating toner band different from the pattern of the spit toner band in this embodiment will be explained.

[0082] First, the reason why the discharged toner band can be formed into a vertical line pattern will be described. The toner in the lubricating toner band is a toner that has little free external additives in the developing device 4 and has a high ability to form an external additive blocking layer on the upstream side of the blade nip portion Q. In other words, the lubricating toner band also plays a role in forming an external additive blocking layer on the upstream side of the blade nip portion Q to suppress the transfer residual toner and the like from passing through the blade 82. Therefore, if the lubricating toner band is formed into a vertical line pattern, a difference will be created in the width of the external additive blocking layer between the vertical line portion (printed portion extending in the direction along the conveying direction) and the vertical space portion (non-printed portion extending in the direction along the conveying direction). In this way, if a portion where the external additive blocking layer is narrow is formed, the transfer residual toner during normal image formation will easily pass through the blade 82 at that portion. In contrast, since the discharged toner band is for discharging deteriorated toner in the developing device 4, the toner in the discharged toner band is mainly deteriorated toner. Deteriorated toner is a toner in which external additives are liberated in the developing device 4, and the ability to form an external additive blocking layer is inherently low. Therefore, there is little difference in the width of the external additive blocking layer between the vertical line portion (printed portion extending in the direction along the transport direction) and the vertical space portion (non-printed portion extending in the direction along the transport direction). For this reason, the band pattern of the spit toner band can be vertical lines. In this way, the spit toner band has the freedom to be provided with non-printed portions extending in the direction along the transport direction.

[0083] Next, the reason why cleaning failure of the discharged toner band can be suppressed even if the pattern of the discharged toner band is a vertical line will be described. FIG. 11 is a graph showing the results of measuring the charge amount of the toner in the lubricating toner band on the intermediate transfer belt 7 and the charge amount of the toner in the discharged toner band on the intermediate transfer belt 7. The charge amount of the toner was calculated by measuring the charge per unit weight (mass) using a suction method that is common in the field. This is a method of measuring the weight [g] and charge amount [μC] of the sucked toner to measure the charge amount [μC / g], and the average charge amount of the toner can be grasped. As shown in FIG. 11, since the toner in the discharged toner band is mainly deteriorated toner, the charge amount of the toner in the discharged toner band on the intermediate transfer belt 7 is low, and the electrostatic adsorption force of the toner in the discharged toner band to the intermediate transfer belt 7 is low. Therefore, the toner in the discharged toner band is easy to clean, which is advantageous in terms of suppressing cleaning failure. Therefore, even if the minimum unit pattern is changed from the horizontal 1 Line-8 Space of Comparative Example 3 to the vertical 2 Line-5 Space of this embodiment, cleaning defects can be suppressed.

[0084] The minimum unit pattern of the lubricating toner band is not limited to the pattern of this embodiment. At least one of the number of dots in the printed portion of the minimum unit pattern and the number of dots in the non-printed portion adjacent to the printed portion may be changed depending on the setting conditions of the blade 82 (contact pressure, etc.), the amount of toner in the lubricating toner band, the fluidity of the toner (type of toner), etc. In this embodiment, the minimum unit pattern composed of the minimum unit dots of the lubricating toner band has a number of dots (minimum unit dot number) of 1 dot (1 line) in the printed portion and 8 dots (8 spaces) in the non-printed portion adjacent to the printed portion in the transport direction. In the minimum unit pattern of the lubricating toner band, the number of dots in the printed portion is preferably 3 / 5 or less (60% or less) of the number of dots in the non-printed portion adjacent to the printed portion in the transport direction, and more preferably 1 / 2 or less (50% or less). As a result, depending on the various conditions described above, a corresponding effect of suppressing cleaning defects can be expected. However, in order to further enhance the effect of suppressing cleaning failure, the minimum unit pattern of the lubricating toner band is preferably such that the number of dots in the printed portion is less than 1 / 2 (less than 50%) of the number of dots in the non-printed portion adjacent to the printed portion in the transport direction, more preferably 2 / 5 or less (40% or less), even more preferably 1 / 3.3 or less (30% or less), and most preferably 1 / 8 or less (12.5% ​​or less). However, in order to suppress a decrease in productivity, the minimum unit pattern of the lubricating toner band is preferably such that the number of dots in the printed portion is more preferably 1 / 20 or more (5% or more) of the number of dots in the non-printed portion adjacent to the printed portion in the transport direction, more preferably 1 / 10 or more (10% or more). In addition, in order to suppress cleaning failure, the minimum unit pattern of the lubricating toner band is preferably such that the number of dots in the continuous printed portion in the transport direction is 4 dots or less, more preferably 2 dots or less, and most preferably 1 dot. As long as the relationship between the number of dots in the printed and non-printed areas is within this range, the printed and non-printed areas may or may not be spaced equally apart.

[0085] In addition, the minimum unit pattern of the discharged toner band is not limited to the pattern of this embodiment. At least one of the number of dots in the printed part of the minimum unit pattern and the number of dots in the non-printed part adjacent to the printed part may be changed depending on the setting conditions of the blade 82 (contact pressure, etc.), the amount of toner in the discharged toner band, the fluidity of the toner (type of toner), etc. In this embodiment, the minimum unit pattern composed of the minimum unit dots of the discharged toner band has a number of dots (minimum unit dot number) of 2 dots (2 lines) in the printed part and a number of dots of 5 dots (5 spaces) in the non-printed part adjacent to the printed part in the longitudinal direction. In the minimum unit pattern of the discharged toner band, the number of dots in the printed part is preferably 3 / 5 or less (60% or less) of the number of dots in the non-printed part adjacent to the printed part in the longitudinal direction, and more preferably 1 / 2 or less (50% or less). As a result, depending on the various conditions described above, a corresponding effect of suppressing cleaning defects can be expected. However, in order to further enhance the effect of suppressing cleaning failure, the minimum unit pattern of the discharged toner band is preferably such that the number of dots in the printed portion in the longitudinal direction is less than 1 / 2 (less than 50%) of the number of dots in the non-printed portion adjacent to the printed portion, and more preferably 2 / 5 or less (40% or less). However, in order to suppress a decrease in productivity, the minimum unit pattern of the discharged toner band is preferably such that the number of dots in the printed portion in the longitudinal direction is more than 1 / 10 (10% or more), and more preferably 1 / 5 or more (20% or more) of the number of dots in the non-printed portion adjacent to the printed portion. Also, in order to suppress a decrease in productivity, the minimum unit pattern of the discharged toner band is preferably such that the number of dots in the printed portion that are consecutive in the longitudinal direction is 2 dots or more. On the other hand, in order to suppress cleaning failure, the minimum unit pattern of the discharged toner band is preferably such that the number of dots in the printed portion that are consecutive in the longitudinal direction is 4 dots or less, more preferably 3 dots or less, and most preferably 2 dots. As long as the relationship between the number of dots in the printed and non-printed areas is within this range, the printed and non-printed areas may or may not be spaced equally apart.

[0086] As described above, the discharged toner band is pushed into the toner accumulation layer as shown in FIG. 7, so that the leading end of the discharged toner band in the transport direction exerts the greatest force on the blade 82. As a result, the toner in the toner accumulation layer and the toner at the leading end of the discharged toner band in the transport direction slip through the blade 82, causing a cleaning failure of about 2 mm in the transport direction. Therefore, the discharged toner band may be formed in a predetermined pattern according to the present embodiment as described above, particularly in the range from the leading end to a position 2 mm toward the rear end in the transport direction. That is, for example, the discharged toner band may be formed in a pattern in which the relationship (aspect ratio) between the length in the transport direction (vertical length W1) and the length in the longitudinal direction (horizontal length W2) of the printed portion when viewed per unit area of ​​1 mm in the transport direction × 1 mm in the longitudinal direction is vertical length W1 > horizontal length W2. In this case, it is preferable that the discharged toner band may be formed in a pattern in which the relationship between the number of dots in the printed portion and the number of dots in the non-printed portion is as described above, in the range from the leading end to a position 2 mm toward the rear end in the transport direction. Also, for the above reasons, the discharged toner band is less likely to cause cleaning defects on the rear end side of the range from the leading edge to the rear end position 2 mm away in the transport direction. Therefore, the discharged toner band may have any pattern on the rear end side of the range from the leading edge to the rear end position 2 mm away in the transport direction. However, in order to minimize the increase in the time required for the discharged toner band formation operation, it is preferable to form the discharged toner band in a pattern in which the amount of toner per unit area (for example, 1 mm in the transport direction x 1 mm in the longitudinal direction) is greater on the rear end side of the range from the leading edge to the rear end position 2 mm away in the transport direction than in the range from the leading edge to the rear end position 2 mm away. Typically, as shown in FIG. 12(a), it is preferable that the discharged toner band is printed with all dots in the transport direction and the longitudinal direction (as a solid image) on the rear end side of the range from the leading edge to the rear end position 2 mm away in the transport direction. As described above, in the configuration of this embodiment, cleaning defects are likely to occur at about 2 mm from the leading edge of the toner band, but this range may change. Therefore, the pattern of the toner band can be changed as described above between a predetermined range where poor cleaning of the leading edge of the toner band is likely to occur and the trailing edge beyond that range.

[0087] The lubricating toner zone generally has a shorter length in the transport direction than the discharged toner zone, so there is little need to change the pattern between the leading end and the trailing end in the transport direction. However, when the length of the lubricating toner zone in the transport direction is longer than 2 mm, the pattern may be changed between the leading end and the trailing end in the transport direction in order to further reduce the time required for the lubricating toner zone formation operation. In this case, the lubricating toner zone may be formed in a predetermined pattern according to the present embodiment as described above, particularly in the range from the leading end to a position 2 mm toward the trailing end in the transport direction. That is, the lubricating toner zone may be formed in a pattern such that the relationship (aspect ratio) between the length in the transport direction (vertical length W1) and the length in the longitudinal direction (horizontal length W2) of the printed portion when viewed per unit area of, for example, 1 mm in the transport direction × 1 mm in the longitudinal direction is vertical length W1 < horizontal length W2. In this case, it is preferable that the lubricating toner zone may be formed in a pattern such that the relationship between the number of dots in the printed portion and the number of dots in the non-printed portion is as described above, in the range from the leading end to a position 2 mm toward the trailing end in the transport direction. The pattern on the rear side of the range 2 mm from the leading edge to the rear edge in the transport direction can be the same as that of the ejected toner band. In other words, the pattern on the rear side of the range 2 mm from the leading edge to the rear edge in the transport direction can be any pattern, such as a pattern with a larger amount of toner per unit area than the range 2 mm from the leading edge (for example, a solid image).

[0088] In this embodiment, the discharged toner band is formed in a pattern in which the printed portion extends substantially parallel to the conveying direction when viewed per unit area of, for example, 1 mm in the conveying direction × 1 mm in the longitudinal direction, but is not limited thereto. The printed portion may be formed in a pattern extending at an angle of ±30° with respect to the conveying direction (FIG. 12(b)). Even when the printed portion extends at such an angle, it is included in the fact that the printed portion extends in a direction along the conveying direction. However, in order to suppress a decrease in productivity, it is preferable that the discharged toner band has a pattern in which the angle between the printed portion and the conveying direction is as small as possible (close to parallel to the conveying direction). Here, consider the case where the direction in which the printed portion of the discharged toner band extends is inclined with respect to the conveying direction. When the direction in which the printed portion extends becomes tilted with respect to the conveying direction, the discharged toner band approaches the state of Comparative Example 3. Then, the discharged toner band approaches a state in which the discharged toner band is supplied to the cleaning blade substantially simultaneously over the entire longitudinal area. This increases the risk of the toner slipping through by pushing up the cleaning blade, and in order to avoid this, it becomes necessary to widen the interval between adjacent printed parts. This leads to a decrease in productivity, as in Comparative Example 3. For this reason, it is preferable that the ejected toner band has a pattern in which the printed part extends at an angle of ±30° with respect to the conveying direction. More preferably, it is preferable that the printed part extends at an angle of ±10° with respect to the conveying direction.

[0089] In addition, the ejected toner band in this embodiment has a long and narrow pattern extending in the transport direction, but a pattern in which square patterns with equal widths in the transport direction and longitudinal direction are arranged in a staggered pattern is considered. In this case, the printed portion becomes close to a pattern extending at an angle of ±45° to the transport direction, which is not preferable as described above.

[0090] Similarly, the lubricating toner band is formed in a pattern in which the printed portion extends substantially parallel to the longitudinal direction when viewed per unit area of, for example, 1 mm in the conveying direction × 1 mm in the longitudinal direction, but is not limited thereto. The printed portion may be formed in a pattern extending at an angle of ±30° with respect to the longitudinal direction (FIG. 12(c)). However, from the viewpoint of uniformly distributing the external additive blocking layer, it is preferable that the lubricating toner band is a pattern in which the printed portion forms as small an angle with the conveying direction as possible (close to parallel to the conveying direction). Even when the printed portion has such an angle, it is included in the printed portion extending in the direction along the longitudinal direction. Note that substantially parallel includes an angle within the margin of error (for example, ±10°).

[0091] In this embodiment, the lubricating toner zone and the spit toner zone are formed over the entire longitudinal area, but the present invention is not limited to this. However, it is desirable that the lubricating toner zone has a sufficient longitudinal length so that lubrication can be imparted over substantially the entire longitudinal area of ​​the blade 82. It is also desirable that the spit toner zone has a sufficient longitudinal length so that the time required for the operation of forming the spit toner zone can be minimized. The longitudinal lengths of the lubricating toner zone and the spit toner zone are desirably 50% or more of the longitudinal length of the image forming area, preferably 80% or more, more preferably 90% or more, and typically approximately 100%.

[0092] In this embodiment, a cleaning device using a swingable blade that is supported to be swingable and pressed against the object to be cleaned by a pressure spring has been described as an example. This configuration has the advantage of stabilizing the pressure of the cleaning blade against the object to be cleaned, but the present invention is not limited to application to a cleaning device with such a configuration. Some cleaning devices use a fixed blade that is fixedly arranged. In a cleaning device using a fixed blade, the contact pressure of the cleaning blade against the object to be cleaned is set depending on the material and fixed position of the cleaning blade. Even in a cleaning device using a fixed blade, there is a possibility that cleaning defects will occur in the toner band (lubricating toner band, ejected toner band) depending on the setting conditions of the cleaning blade (contact pressure, etc.), the amount of toner in the toner band, the fluidity of the toner (type of toner), etc. Therefore, the present invention is also effective for a cleaning device using a fixed blade.

[0093] Although the belt cleaning device 8 has been described in this embodiment, this embodiment is also effective in the case where the toner band is supplied to the edge portion of the cleaning blade of the drum cleaning device 6. That is, in order to suppress the occurrence of abnormal noise and curling due to poor sliding between the cleaning blade of the drum cleaning device 6 and the photosensitive drum 1, an operation of forming a lubricating toner band and supplying it to the edge portion of the cleaning blade may be performed. Also, the spit toner band may be conveyed to the drum cleaning device 6 without being primarily transferred to the intermediate transfer belt 7. In this case, too, by making the pattern of the toner band (lubricating toner band, spit toner band) conform to the pattern of this embodiment, the same effect as this embodiment can be obtained.

[0094] Thus, in this embodiment, the image forming apparatus 100 includes a rotatable image carrier (intermediate transfer belt) 7 that carries a toner image, a developing device 4 that develops an electrostatic image with toner, an image forming means (image forming section) P that forms a toner image on the image carrier, a transfer means (secondary transfer roller) 9 that transfers the toner image formed on the image carrier 7 to a recording material S, a cleaning blade 82 that comes into contact with the image carrier 7 along a second direction (longitudinal direction) that is approximately perpendicular to a first direction (transport direction) that is the moving direction of the surface of the image carrier 7, and removes toner from the image carrier 7, and a toner image forming means (image forming section) that, based on an index value that correlates with the printing rate of the toner image formed on the image carrier 7, and a control unit 200 that controls to execute a predetermined operation (discharged toner band forming operation) of forming a predetermined toner image (discharged toner band) on the image carrier 7 along the second direction that is not transferred to the recording material S, and removing the predetermined toner image from the image carrier 7 by the cleaning blade 82, and the predetermined toner image is formed by repeating a printed portion extending along the first direction and a non-printed portion extending along the first direction adjacent to the printed portion, at least in a predetermined range of the tip end in the first direction, when viewed per unit area of ​​1 mm in each of the first direction and the second direction. In this embodiment, the predetermined toner image satisfies a relationship W1>W2 between the length W1 of the printed portion in the first direction and the length W2 in the second direction, at least in the predetermined range, when viewed per unit area. Also, in this embodiment, the predetermined toner image is formed such that the printed portion is approximately parallel to the first direction when viewed per unit area, at least in the predetermined range. Also, in this embodiment, the predetermined toner image is formed such that a minimum unit pattern is repeated in the first direction and the second direction, at least in the predetermined range, and the minimum unit pattern is formed such that, in the second direction, the number of dots in the printed portion is typically less than 1 / 2 the number of dots in the non-printed portion adjacent to the printed portion, and preferably the number of dots in the printed portion is 2 / 5 or less the number of dots in the non-printed portion adjacent to the printed portion, and in this embodiment, the number of dots in the printed portion is 2 dots, and the number of dots in the non-printed portion adjacent to the printed portion is 5 dots.The predetermined toner image may be formed to have a first region in the predetermined range and a second region on the rear end side of the predetermined range in the first direction, in which case the toner amount per unit area of ​​the second region can be greater than the toner amount per unit area of ​​the first region. Typically, the second region is formed as a solid image. In this embodiment, the predetermined range is a range from the leading end to a position 2 mm toward the rear end side in the first direction of the predetermined toner image. In this embodiment, the predetermined toner image is formed over substantially the entire image forming region in the second direction.

[0095] Further, in the present embodiment, the control unit 200 can control to execute a first operation (discharge toner band forming operation) for forming a predetermined first toner image (discharge toner band) that is not transferred to the recording material S, and a second operation (lubricating toner band forming operation) for forming a predetermined second toner image (lubricating toner band) that is not transferred to the recording material S. The first toner image is formed by repeating, at least in the predetermined range, a printing portion extending along the first direction and a non-printing portion extending along the first direction adjacent to the printing portion when viewed per unit area. The second toner image is formed by repeating, at least in the predetermined range, a printing portion extending along the second direction and a non-printing portion extending along the second direction adjacent to the printing portion when viewed per unit area. In the present embodiment, in the first toner image, at least in the predetermined range, when viewed per unit area, the relationship between the length W1 in the direction along the first direction of the printing portion and the length W2 in the direction along the second direction satisfies W1>W2. In the second toner image, at least in the predetermined range, when viewed per unit area, the relationship between the length W1 in the direction along the first direction of the printing portion and the length W2 in the direction along the second direction satisfies W1<W2. Further, in the present embodiment, the first toner image is formed to have a first region within the predetermined range and a second region on the rear end side of the predetermined range in the first direction. The second toner image is formed such that the entire length from the front end to the rear end in the first direction is included in the predetermined range.

[0096] As described above, according to the present embodiment, it is possible to suppress a decrease in productivity and suppress cleaning failure of the discharge toner band. Further, according to the present embodiment, the pattern of the toner band, specifically, the aspect ratio of the pattern of the toner band, is changed according to the type of the toner band (lubricating toner band, discharge toner band). Thereby, it is possible to suppress cleaning failure of the toner band according to the type of the toner band, and it is possible to minimize a decrease in productivity due to an increase in the time required for the toner band forming operation according to the type of the toner band.

[0097] [Example 2] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are given the same reference numerals as those of embodiment 1, and detailed explanations are omitted.

[0098] In this embodiment, the pattern of the spit toner band is changed according to the degree of deterioration of the toner in the developing device 4. In other words, when a low-print rate image with a low print rate is continuously formed and the operation of forming the spit toner band is frequently performed, the charge amount of the toner decreases due to toner deterioration, making it easier to clean the toner in the spit toner band, which is advantageous in preventing cleaning failures. In such a case, even if the number of vertical lines, which is the printing portion of the spit toner band, is increased, it is possible to prevent the toner in the spit toner band from slipping through the blade 82.

[0099] In this embodiment, the pattern of the discharged toner band is changed based on the information of the execution history of the discharged toner band formation operation, thereby making it possible to further reduce the time required for the discharged toner band formation operation. For example, the pattern of the discharged toner band can change at least one of the number of dots in the printed part and the number of dots in the non-printed part of the minimum unit pattern.

[0100] FIG. 13 is a schematic block diagram showing the control mode of the image forming apparatus 100 of this embodiment. The control mode in this embodiment shown in FIG. 13 is generally similar to the control mode in the first embodiment shown in FIG. 4. However, in this embodiment, the control unit 200 is provided with an execution history recording unit 203 that records (stores) information on the execution history of the discharged toner band. In this embodiment, the execution history recording unit 203 records information on the determination result of necessity each time the control for determining the necessity of the discharged toner band formation operation described with reference to FIG. 5 is executed, information on the number of times the discharged toner band formation operation is executed in a predetermined period, and the like. This predetermined period may be, for example, a period for a predetermined number of times of control for determining the necessity of the discharged toner band formation operation until the current control, or a period from the beginning of use of the developing device 4 to the current control. In this embodiment, the execution history recording unit 203 is realized by a CPU and a non-volatile memory.

[0101] Fig. 14 is a flow chart of the control of the spit toner band pattern in this embodiment. Note that, although the description here focuses on one image forming unit P as a representative, similar control is performed for each image forming unit P. Also, for simplicity, the description here will be omitted regarding the control for determining whether or not the spit toner band forming operation is required, as described with reference to Fig. 5, and will focus on the selection of a pattern when the spit toner band forming operation is performed.

[0102] When the control unit 200 executes the operation of forming the discharged toner band after accepting a job (S301), it acquires information on the execution history of the operation of forming the discharged toner band from the execution history recording unit 203 (S302). Next, the control unit 200 judges whether the operation of forming the discharged toner band has been executed consecutively a predetermined threshold value or more up to the current control based on the information on the execution history of the operation of forming the discharged toner band (S303). Here, the operation of forming the discharged toner band is executed consecutively means that the operation of forming the discharged toner band is judged to be necessary in the control for judging the necessity of the operation of forming the consecutive discharged toner bands, and the forming operation is executed. Then, when the control unit 200 judges in S303 that the operation of forming the discharged toner band has been executed consecutively a threshold value or more, the number of vertical lines of the discharged toner band is increased from, for example, 2 vertical lines to 3 vertical lines (i.e., 3 vertical lines-5 spaces), and the length of the discharged toner band in the conveying direction is shortened by the amount of the increase in the number of vertical lines to form the discharged toner band (S304).

[0103] If the control unit 200 determines in S303 that the operation of forming the discharged toner band has not been performed consecutively a number of times equal to or greater than the threshold, it determines whether the number of times the operation of forming the discharged toner band has been performed, not consecutively, during a predetermined period up to the current control is equal to or greater than a predetermined threshold, based on information on the execution history of the operation of forming the discharged toner band (S305).If the control unit 200 determines in S305 that the operation of forming the discharged toner band has been performed a number of times equal to or greater than the threshold, it reduces the number of vertical spaces in the discharged toner band, for example, from 5 spaces to 4 spaces (i.e., 2 vertical lines - 4 spaces), and shortens the length of the discharged toner band in the transport direction by the amount of the reduction in the number of vertical spaces to form the discharged toner band (S306).

[0104] Furthermore, if the control unit 200 determines in S305 that the ejected toner band formation operation has not been performed a number of times equal to or greater than the threshold value, it forms an ejected toner band with the normal number of vertical lines, number of vertical spaces, and length in the transport direction of an ejected toner band (e.g., 2 vertical lines - 5 spaces, and a transport direction length of 420 mm) (S307).

[0105] In this embodiment, the pattern of the discharged toner band is changed in S304, S306, and S307. The discharged toner band formed in S304 (vertical 3 lines-5 spaces), the discharged toner band formed in S306 (vertical 2 lines-4 spaces), and the discharged toner band formed in S307 (vertical 2 lines-5 spaces) are longer in the transport direction in this order. However, the present invention is not limited to this embodiment, and the pattern of the discharged toner band may be changed only depending on whether the discharged toner band forming operation has been performed a predetermined number of times or more in succession. In this way, the ratio D1 / D2 of the number of dots D1 of the printed part in the longitudinal direction of the minimum unit pattern of the discharged toner band to the number of dots D2 of the non-printed part adjacent to the printed part can be changed according to the index value indicating the degree of deterioration of the toner in the developing device 4. Information on the frequency of the discharged toner band forming operation can be used as the index value indicating the degree of deterioration of the toner in the developing device 4. The information on the frequency of execution of the spit toner band forming operation can be, for example, the number of times the spit toner band forming operation is executed per unit number of images formed, the number of times the spit toner band forming operation is executed consecutively, etc. The higher the execution frequency, the larger the ratio D1 / D2 can be.

[0106] Thus, in this embodiment, the predetermined toner image (discharged toner band) is formed by repeating the minimum unit pattern in the first direction (transport direction) and the second direction (longitudinal direction) at least in a predetermined range of the leading end in the first direction (transport direction), and the control unit 200 can change at least one of the number of dots in the printed part of the minimum unit pattern in the second direction and the number of dots in the non-printed part adjacent to the printed part based on information on the execution history of the predetermined operation (discharged toner band forming operation). In this embodiment, the control unit 200 can change at least one of the number of dots in the printed part and the number of dots in the non-printed part so that the ratio D1 / D2 of the number of dots D1 in the printed part to the number of dots D2 in the non-printed part is set to a first value when the number of executions of the predetermined operation per unit image formation sheet number indicated by the information on the execution history is a first number, and the ratio D1 / D2 is set to a second value larger than the first value when the number of executions is a second number larger than the first number.

[0107] As described above, according to this embodiment, it is possible to suppress poor cleaning of the spit toner band, and to further suppress a decrease in productivity by shortening the time required for the operation of forming the spit toner band as much as possible.

[0108] [others] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-mentioned embodiments.

[0109] In the above embodiment, the image forming apparatus is a tandem-type full-color image forming apparatus, but the present invention is not limited to this. The image forming apparatus is not limited to a tandem-type image forming apparatus, and may be an image forming apparatus of another type, such as a configuration in which a plurality of color toner images are sequentially formed on one photoconductor, each toner image is superimposed on an intermediate transfer body and then primarily transferred onto a recording material, and then secondarily transferred onto a recording material. In addition, the image forming apparatus is not limited to being a full-color image forming apparatus, and may be, for example, a monochrome image forming apparatus of a single color, black. In addition, the image forming apparatus may be implemented for various purposes, such as a printer, various printing machines, copiers, FAX machines, and multifunction machines.

[0110] In addition, in this embodiment, a pattern in which non-printed parts and printed parts are alternately repeated in the longitudinal direction of the cleaning blade has been described, but the present invention is not limited thereto. For example, a pattern in which high-density printed parts close to a solid density and low-density printed parts that are low-density halftones are alternately repeated may be used. In this case, the relationship between the number of dots in the high-density printed parts and the low-density printed parts may be formed in a pattern similar to the relationship between the number of dots in the printed parts and the number of dots in the non-printed parts described above. In other words, the discharged toner band may be formed in a predetermined range at least at the tip end in the first direction (transport direction), when viewed per unit area of ​​1 mm in each of the first direction (transport direction) and the second direction (longitudinal direction), by repeating a high-density printed part that is formed at a higher density than the average density of the unit area and extends along the first direction (transport direction), and a low-density printed part that is a low-density printed part that is lower in density than the average density of the unit area and extends along the first direction (transport direction) adjacent to the high-density printed part. Furthermore, the lubricating toner band may be formed in at least a predetermined range of the tip end in a first direction (transport direction), when viewed per unit area of ​​1 mm in each of the first direction (transport direction) and the second direction (longitudinal direction), at a concentration higher than the average concentration of the unit area, and may be formed by repeating a high-density printed portion extending along the second direction (longitudinal direction) and a low-density printed portion having a concentration lower than the average concentration of the unit area, the low-density printed portion extending along the second direction (longitudinal direction) adjacent to the high-density printed portion. [Explanation of symbols]

[0111] 1 Photosensitive drum 2. Charge roller 3. Exposure equipment 5 Primary transfer roller 6 Drum cleaning device 7 Intermediate transfer belt 8 Belt cleaning device 82 Cleaning blade

Claims

1. A rotatable image carrier for carrying a toner image, A developing apparatus for developing an electrostatic image with toner, comprising an image forming unit that forms a toner image on the image carrier, A transfer unit that transfers the toner image on the image carrier to a recording material, A cleaning blade for removing toner from the image carrier, The system includes a control unit that controls the system to perform a predetermined operation to form a predetermined toner image on the image carrier that is not transferred to the recording material, and then remove the predetermined toner image from the image carrier using the cleaning blade, At least, in a predetermined range of the leading edge of the predetermined toner image in a first direction which is the direction of movement of the surface of the image carrier, when viewed per unit area of ​​1 mm in both the first direction and the second direction which is the width direction of the image carrier perpendicular to the first direction, the predetermined toner image includes a plurality of printed portions that extend along the predetermined direction and are formed at different positions in the second direction, and the angle between the predetermined direction and the first direction is 30° or less. An image forming apparatus characterized in that, at least within the predetermined range, each printing section is a linear toner strip formed substantially continuously over substantially the entire area with respect to the first direction.

2. In at least the predetermined range, the predetermined toner image includes a plurality of non-printing portions provided adjacent to each of the printing portions at different positions in the second direction and extending along the predetermined direction, The image forming apparatus according to claim 1, characterized in that, with respect to the second direction, the width Wa of each printed portion is narrower than the width Wb of each non-printed portion.

3. With respect to the second direction, the width Wa and the width Wb have the following relationship: 1 / 10≦Wa / Wb<3 / 5 The image forming apparatus according to claim 2, characterized in that it satisfies the requirements.

4. With respect to the second direction, the width Wa and the width Wb have the following relationship: 1 / 5≦Wa / Wb<2 / 5 The image forming apparatus according to claim 2, characterized in that it satisfies the requirements.

5. The image forming apparatus according to claim 1, characterized in that, with respect to the second direction, the number of consecutive dots in each of the printed sections is 4 dots or less.

6. The image forming apparatus according to claim 1, characterized in that, with respect to the second direction, the number of consecutive dots in each of the printed sections is 3 dots or less.

7. The image forming apparatus according to claim 1, characterized in that, with respect to the second direction, the number of consecutive dots in each of the printed sections is two dots.

8. The image forming apparatus according to claim 1, characterized in that the control unit performs the predetermined operation based on an index value that correlates with the printing rate of the toner image formed on the image carrier.

9. The image forming apparatus according to claim 1, characterized in that the angle between the predetermined direction and the first direction is 10° or less.

10. The image forming apparatus according to claim 1, characterized in that the predetermined direction is parallel to the first direction.

11. The predetermined toner image is formed to include a first region within the predetermined range and a second region located further to the rear end than the predetermined range in the first direction. The image forming apparatus according to claim 1, characterized in that the amount of toner per unit area of ​​the second region is greater than the amount of toner per unit area of ​​the first region.

12. The image forming apparatus according to claim 11, characterized in that the second region is formed by a solid image.

13. The image forming apparatus according to claim 1, characterized in that the predetermined range is the range from the leading edge of the predetermined toner image in the first direction to a position 2 mm from the leading edge toward the rear end in the first direction.

14. The predetermined toner image is formed in which the smallest unit pattern is repeated in the first direction and the second direction, at least within the predetermined range. The image forming apparatus according to claim 1, characterized in that the control unit can change at least one of the number of dots in each of the printed portions in the second direction of the minimum unit pattern and the number of dots in each of the non-printed portions adjacent to the printed portions in the second direction of the minimum unit pattern, based on information of the execution history of the predetermined operation.

15. The image forming apparatus according to claim 14, wherein the control unit can change at least one of the number of dots in each printed area and the number of dots in each non-printed area, such that when the number of executions of the predetermined operation per unit number of formed images indicated by the execution history information is a first number of executions, the ratio (D1 / D2) of the number of dots in each printed area to the number of dots D2 of each non-printed area is set to a first value, and when the number of executions is a second number of executions which is greater than the first number of executions, the ratio D1 / D2 is set to a second value which is greater than the first value.

16. The image forming apparatus according to claim 1, characterized in that the predetermined toner image is formed over substantially the entire area of ​​the image forming region in the second direction.

17. A rotatable image carrier for holding a toner image, A developing apparatus for developing an electrostatic image with toner, comprising an image forming unit that forms a toner image on the image carrier, A transfer unit that transfers the toner image on the image carrier to a recording material, A cleaning blade for removing toner from the image carrier, The system includes a control unit that controls the system to perform a first operation in which a first toner image that is not transferred to the recording material is formed on the image carrier, and then the first toner image is removed from the image carrier by the cleaning blade, and a second operation in which a second toner image that is not transferred to the recording material is formed on the image carrier, and then the second toner image is removed from the image carrier by the cleaning blade, At least, in a predetermined range of the leading edge of the first toner image in a first direction which is the direction of movement of the surface of the image carrier, when viewed per unit area of ​​1 mm in both the first direction and the second direction which is the width direction of the image carrier perpendicular to the first direction, the first toner image includes a plurality of first printing portions that extend along the first predetermined direction and are formed at different positions in the second direction, and the angle between the first predetermined direction and the first direction is 30° or less. At least, in a predetermined range of the leading edge of the second toner image in the first direction, which is the direction of movement of the surface of the image carrier, when viewed per unit area of ​​1 mm in both the first and second directions, the second toner image includes a plurality of second printing portions that extend along the second predetermined direction and are formed at different positions in the first direction, and the angle between the second predetermined direction and the second direction is 30° or less. At least within the predetermined range, each of the first printing sections is a linear toner strip formed substantially continuously over substantially the entire area with respect to the first direction. An image forming apparatus characterized in that, at least within the predetermined range, each of the second printing portions is a linear toner strip formed substantially continuously over substantially the entire area with respect to the second direction.

18. The image forming apparatus according to claim 17, characterized in that the first toner image is a toner image formed to refresh the toner in the developing apparatus, and the second toner image is a toner image to be supplied to the contact portion of the cleaning blade.

19. The image forming apparatus according to claim 17, characterized in that the first operation is performed based on a first index value correlated with the printing rate of the toner image formed on the image carrier, and the second operation is performed based on a second index value correlated with the number of images formed, regardless of the first index value.

20. In at least the predetermined range, the first toner image includes a plurality of first non-printing portions provided adjacent to each of the first printing portions at different positions in the second direction and extending along the first predetermined direction, The image forming apparatus according to claim 17, characterized in that, with respect to the second direction, the width W11 of each of the first printed portions is narrower than the width W12 of each of the first non-printed portions.

21. The second toner image includes a plurality of second non-printing portions provided adjacent to each of the second printing portions at different positions in the first direction and extending along the second predetermined direction, The image forming apparatus according to claim 17, characterized in that, with respect to the first direction, the width W21 of each of the second printing portions is narrower than the width W22 of each of the second non-printing portions.

22. With respect to the second direction, the width W11 and the width W12 have the following relationship: 1 / 10≦W11 / W12<3 / 5 The image forming apparatus according to claim 20, characterized in that it satisfies the following conditions.

23. With respect to the second direction, the width W11 and the width W12 have the following relationship: 1 / 5≦W11 / W12<2 / 5 The image forming apparatus according to claim 20, characterized in that it satisfies the following conditions.

24. With respect to the first direction, the width W21 and the width W22 have the following relationship: 1 / 10≦W21 / W22<3 / 5 The image forming apparatus according to claim 21, characterized in that it satisfies the following conditions.

25. With respect to the first direction, the width W21 and the width W22 have the following relationship: 1 / 5≦W21 / W22<2 / 5 The image forming apparatus according to claim 21, characterized in that it satisfies the following conditions.

Images