JP7703327B2 - Image forming device - Google Patents

Description

The present invention relates to image forming devices such as copying machines, printers, and facsimile machines that use electrophotographic or electrostatic recording methods.

Conventionally, as an image forming apparatus using electrophotography, as typified by laser printers and copiers, there is an image forming apparatus using an intermediate transfer method in which a toner image formed on an image carrier is primarily transferred onto an intermediate transfer body, and then secondarily transferred onto a recording material such as recording paper. As the intermediate transfer body, an intermediate transfer belt, which is an endless belt that can rotate in contact with the image carrier, is often used.

One of the challenges in achieving high image quality in such image forming devices is improving the primary transferability. Specifically, it is necessary to reduce the amount of primary transfer residual toner remaining on the image carrier when the toner image formed on the image carrier is primarily transferred onto the intermediate transfer belt. To improve this primary transferability, a technique is known in which a speed difference (circumferential speed difference) is established between the peripheral speed of the image carrier and the peripheral speed of the intermediate transfer belt.

Here, if there is a difference in peripheral speed between the image carrier and the surface of the intermediate transfer belt, a frictional force is generated based on the difference in the friction coefficient between the two. As a result, the frictional force changes depending on whether or not there is toner that functions as a lubricant between the image carrier and the intermediate transfer belt, causing the rotational speed of the image carrier to fluctuate. This causes the exposure to the image carrier to become blurred, and streaky image defects (herein also referred to as "exposure blur") may occur at the leading edge of the image.

As a technique for suppressing the above-mentioned exposure blur, a technique for forming a lubricating toner image in the non-image area has been proposed (Patent Document 1).

JP 2004-118076 A

However, in the previously proposed technology for forming a lubricating toner image, the lubricating toner image was formed at a predetermined printing rate across the entire width of the image area in the main scanning direction. This resulted in a problem of a large amount of toner being consumed to form the lubricating toner image.

Therefore, the present invention aims to suppress the occurrence of exposure blur while suppressing the consumption of toner used to form the lubricating toner image.

The above object is achieved by an image forming apparatus according to the present invention. In summary, according to one aspect of the present invention, an image forming apparatus for forming a toner image on a recording material includes an image forming section for forming the toner image on an image carrier, an intermediate transfer body which is a movable intermediate transfer body that contacts the image carrier to form a primary transfer section, and in which an image portion is formed in an image formable area corresponding to an area on the recording material where the toner image can be formed by a first toner image which is the toner image primarily transferred from the image carrier in the primary transfer section, and a control section which controls to form a second toner image which is the toner image for lubrication in a non-image area in the image formable area of the intermediate transfer body where the first toner image of a print image based on image information is not formed , and the control section controls to control a second toner image which is the toner image for lubrication in a non-image area in which the first toner image of the print image based on image information is not formed, and the control section controls a second toner image which is the toner image for lubrication in a non-image area in which the image portion of the intermediate transfer body is formed and in which the second toner image ... an image forming apparatus that performs control so that the second toner image is not formed in an area of the non-image area that overlaps with an area in which the image area is formed when viewed in the moving direction , and performs control so that the second toner image is formed in the first non-image area in a state in which a first non-image area, which is the non-image area, is formed downstream of the image area in the moving direction of the surface of the intermediate transfer body; the control unit performs control to change the size of the area in which the second toner image is formed based on the image information, and performs control so that the second toner image formed in the first non-image area has the same width as the first toner image formed in the image area or has a width that is located more inward than the first toner image in the width direction, and is not formed outside the first toner image .
According to another aspect of the present invention, an image forming apparatus for forming a toner image on a recording material includes an image forming unit for forming the toner image on an image carrier, an intermediate transfer body which is in contact with the image carrier to form a primary transfer unit and is movable, the intermediate transfer body having an image portion formed in an image formable region corresponding to a region on the recording material where the toner image can be formed by a first toner image which is the toner image primarily transferred from the image carrier in the primary transfer unit, and a control unit which controls to form a second toner image which is the toner image for lubrication in a non-image portion which is a region in the image formable region of the intermediate transfer body where the first toner image of a print image based on image information is not formed, and the control unit controls to form a second toner image which is the toner image for lubrication in the region of the intermediate transfer body where the image portion is formed and in the region of the non-image portion which overlaps with the region where the image portion is formed when viewed in a width direction of the intermediate transfer body which is perpendicular to a moving direction of the surface of the intermediate transfer body. and controls the amount of toner in the second toner image in a first region close to the image portion in the first non-image portion in a state in which a first non-image portion, which is the non-image portion, is formed downstream of the image portion in the moving direction of the surface of the intermediate transfer body, so that the amount of toner in the second toner image in a first region close to the image portion in the first non-image portion is greater than the amount of toner in the second region in the first non-image portion farther from the image portion in the first non-image portion than the first region, and controls the amount of toner in the second toner image in the width direction so that the second toner image formed in the first non-image portion has the same width as the width of the first toner image formed in the image portion or has a width located inside the first toner image, and is not formed outside the first toner image.

According to the present invention, it is possible to suppress the occurrence of exposure blur while suppressing the consumption of toner used to form the lubricating toner image.

FIG. 1 is a schematic cross-sectional view of an image forming apparatus. FIG. 2 is a schematic cross-sectional view of a photosensitive drum. FIG. 2 is a schematic cross-sectional view of an intermediate transfer belt. FIG. 1 is a schematic cross-sectional view of a surface torque measuring device. FIG. 2 is a schematic diagram of an embodiment of a lubricating toner image (a pattern of minute dots). FIG. 11 is a graph showing the correlation between the width of a print image and the level of exposure blur. FIG. 4 is a schematic diagram showing an example of a lubricating toner image. 11A and 11B are schematic diagrams illustrating other examples of lubricating toner images. 11A and 11B are schematic diagrams illustrating other examples of lubricating toner images. 11A and 11B are schematic diagrams illustrating other examples of lubricating toner images. 11A and 11B are schematic diagrams illustrating other examples of lubricating toner images. 11A and 11B are schematic diagrams illustrating other examples of lubricating toner images. 11A and 11B are schematic diagrams illustrating other examples of lubricating toner images. FIG. 4 is a schematic diagram showing a lubricating toner image of Comparative Example 1. 5A and 5B are schematic diagrams for explaining a mode of forming a lubricating toner image. FIG. 2 is a schematic diagram showing an example of a lubrication image. FIG. 2 is a schematic diagram showing an example of a lubrication image. FIG. 2 is a schematic diagram showing an example of a lubrication image.

The image forming apparatus according to the present invention will be described in more detail below with reference to the drawings.

[Example 1]
1 is a schematic cross-sectional view of an image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 according to the present embodiment is a tandem type (in-line type) laser beam printer that employs an intermediate transfer method and is capable of forming full-color images using an electrophotographic method.

The 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 toner images of the respective colors of yellow (Y), magenta (M), cyan (C) and black (K). Elements having the same or corresponding functions or configurations in each image forming unit PY, PM, PC and PK may be generally described by omitting the Y, M, C and K at the end of the reference numerals indicating that the element is for one of the colors. In this embodiment, the image forming unit P is configured with the photosensitive drum 1 (1Y, 1M, 1C, 1K), charging roller 2 (2Y, 2M, 2C, 2K), exposure device 3 (3Y, 3M, 3C, 3K), developing device 4 (4Y, 4M, 4C, 4K), primary transfer roller 5 (5Y, 5M, 5C, 5K), drum cleaning device 6 (6Y, 6M, 6C, 6K) and the like, which will be described later.

The photosensitive drum 1, which is a rotatable drum-shaped (cylindrical) electrophotographic photosensitive body (photoconductor) as an image carrier that carries a toner image, is rotated in the direction of the arrow R1 in the figure (clockwise) at a predetermined rotation speed (circumferential speed) described later. The surface of the rotating photosensitive drum 1 is charged to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by a charging roller 2, which is a roller-shaped charging member as a charging means. During charging, a predetermined charging voltage (charging bias) is applied to the charging roller 2. The surface of the charged photosensitive drum 1 is scanned and exposed based on an image signal by an exposure device (laser scanner unit) 3 as an exposure means, and an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 1. The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) by the developing device 4 as a developing means, which supplies toner as a developer, and a toner image is formed on the photosensitive drum 1. The developing device 4 has a developing roller 41 as a developer carrier and a toner container 42 that contains toner. During development, a predetermined development voltage (development bias) is applied to the development roller 41. In this embodiment, toner charged with the same polarity as the charge polarity of the photosensitive drum 1 (negative polarity in this embodiment) adheres to the exposed portion of the photosensitive drum 1, where the absolute value of the potential has been reduced by exposure after being uniformly charged (reverse development).

An intermediate transfer belt 8 made of an endless belt is arranged so as to be movable (rotatable) in contact with each photosensitive drum 1 of each image forming unit P. The intermediate transfer belt 8 is an example of an intermediate transfer body that conveys a toner image transferred from an image carrier to a transfer material for secondary transfer. The intermediate transfer belt 8 is stretched around a driving roller 9 and a driven roller 10 as a plurality of tension rollers (support members) and stretched with a predetermined tension. The intermediate transfer belt 8 rotates (moves in a circular motion) in the direction of arrow R2 (counterclockwise) in the figure at a peripheral speed (surface movement speed) corresponding to the peripheral speed (surface movement speed) of the photosensitive drum 1 by the driving roller 9 being driven to rotate. In this embodiment, the surface movement speed (peripheral speed, process speed) of the intermediate transfer belt 8 is 210 mm/sec. On the inner peripheral surface side of the intermediate transfer belt 8, a primary transfer roller 5, which is a roller-shaped primary transfer member as a primary transfer means, is arranged corresponding to each photosensitive drum 1. The primary transfer roller 5 is pressed against the photosensitive drum 1 via the intermediate transfer belt 8, forming a primary transfer portion N1 where the photosensitive drum 1 and the intermediate transfer belt 8 come into contact. As described above, the toner image formed on the photosensitive drum 1 is primarily transferred to the rotating intermediate transfer belt 8 at the primary transfer portion N1. During the primary transfer, a primary transfer voltage (primary transfer bias), which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner (charging polarity of the toner during development), is applied to the primary transfer roller 5. For example, when a full-color image is formed, the toner images of yellow, magenta, cyan, and black formed on each of the photosensitive drums 1Y, 1M, 1C, and 1K are sequentially primarily transferred so as to be superimposed on the intermediate transfer belt 8.

On the outer peripheral surface side of the intermediate transfer belt 8, a secondary transfer roller 11, which is a roller-shaped secondary transfer member serving as a secondary transfer means, is disposed at a position facing the drive roller 9, which also serves as a secondary transfer opposing roller. The secondary transfer roller 11 is pressed against the drive roller 9 via the intermediate transfer belt 8, forming a secondary transfer section N2 where the intermediate transfer belt 8 and the secondary transfer roller 11 come into contact with each other. The toner image formed on the intermediate transfer belt 8 as described above is secondarily transferred onto a transfer material (recording material, sheet) S, such as a recording paper, which is sandwiched and conveyed between the intermediate transfer belt 8 and the secondary transfer roller 11 in the secondary transfer section. During the secondary transfer, a secondary transfer voltage (secondary transfer bias), which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, is applied to the secondary transfer roller 11. The transfer material S is stored in a transfer material cassette 13, fed from the transfer material cassette 13 by a feed roller 14 of the feed conveying device 12, and conveyed to a registration roller pair 16 by a conveying roller pair 15 of the feed conveying device 12. The transfer material S is then supplied to the secondary transfer section N2 by the registration roller pair 16 in synchronization with the toner image on the intermediate transfer belt 8.

The transfer material S onto which the toner image has been transferred is transported to a fixing device 17 as a fixing means. The fixing device 17 heats and presses the transfer material S carrying the unfixed toner image, thereby fixing (melting and adhering) the toner image to the surface of the transfer material S. The transfer material S is then discharged (output) by a pair of discharge rollers 18 onto a discharge tray 50 provided outside the device body 110 of the image forming device 100.

In addition, primary transfer residual toner that is not transferred to the intermediate transfer belt 8 during the primary transfer and remains on the photosensitive drum 1 is removed from the photosensitive drum 1 and collected by the drum cleaning device 6 as a photosensitive body cleaning means. The drum cleaning device 6 has a drum cleaning blade 61 as a cleaning member and a collected toner container 62. The drum cleaning device 6 scrapes off the primary transfer residual toner from the surface of the rotating photosensitive drum 1 with the drum cleaning blade 61 and stores it in the collected toner container 62. In addition, toner (secondary transfer residual toner) that is not transferred to the transfer material S during the secondary transfer and remains on the intermediate transfer belt 8 is removed from the intermediate transfer belt 8 and collected by the belt cleaning device 20 as an intermediate transfer body cleaning means. The belt cleaning device 20 has a belt cleaning blade 21 as a cleaning member and a collected toner container 22. The belt cleaning device 20 scrapes off the secondary transfer residual toner from the surface of the rotating intermediate transfer belt 8 with the belt cleaning blade 21 and stores it in the collected toner container 22.

The image forming apparatus 100 also has a control unit (controller) 80. The control unit 80 is configured with a CPU as an arithmetic control means, memories such as ROM and RAM as storage means, and an input/output circuit that controls the input and output of signals between the control unit 80 and each unit. The control unit 80 comprehensively controls the operation of each unit of the image forming apparatus 100 by the CPU executing processing based on programs and data stored in the memory. The control unit 80 controls each unit of the image forming apparatus 100 to perform image formation based on image information input from an external device such as an image reading device or a personal computer connected to the image forming apparatus 100.

In this embodiment, in each image forming station P, the photosensitive drum 1 and the charging roller 2 acting on it as process means, the developing device 4, and the drum cleaning device 6 constitute a process cartridge 7 that is detachable from the device main body 110. In this embodiment, the intermediate transfer belt 8, the drive roller 9, the driven roller 10, the primary transfer rollers 5Y, 5M, 5C, 5K, etc. constitute an intermediate transfer unit 30 that is detachable from the device main body 110.

The toner used in this embodiment is a nearly spherical toner (one-component non-magnetic developer) with an average particle size of 5 to 8 μm. In this embodiment, a total of two transfers, a primary transfer and a secondary transfer, are performed, so a spherical toner with good transferability is used as the toner. The toner used in this embodiment is manufactured by a polymerization method. This toner becomes nearly spherical due to the manufacturing method. In addition, the toner used in this embodiment contains wax in the core, and styrene-butyl acrylate is used for the binder resin layer on the core, and styrene-polyester is used for the outermost resin layer on top of that. In addition, an external additive is added to the toner to stabilize the charging performance and provide lubricity. Note that vinyl copolymers made of styrene-based resins and acrylic-based resins, polyester resins, etc. can be used as the binder resin for the toner.

2. Photosensitive Drum Next, the photosensitive drum 1 will be described.

The photosensitive drum 1 generally has a conductive support 1a and a photosensitive layer 1b formed on the support 1a. The photosensitive layer 1b may be a single-layer type photosensitive layer containing a charge transport material and a charge generation material in the same layer, or may be a laminated type photosensitive layer formed by laminating a charge generation layer 1b1 containing a charge generation material and a charge transport layer 1b2 containing a charge transport material. Figure 2 shows the layer structure of a laminated type photosensitive drum 1. In this embodiment, a laminated type photosensitive drum 1 is used. A protective layer 1c may also be provided on the photosensitive layer 1b. In this embodiment, the photosensitive drum 1 is provided with a protective layer 1c. The surface layer of the photosensitive drum 1 is the layer located on the outermost surface side of the photosensitive drum 1. In other words, the surface layer of the photosensitive drum 1 is the layer furthest from the support 1a and has a surface that carries toner. Therefore, in this embodiment, the surface layer of the photosensitive drum 1 is the protective layer 1c.

In this embodiment, the surface layer of the photosensitive drum 1 (protective layer 1c in this embodiment) contains acrylic resin (polymer of acrylic acid ester or methacrylic acid ester). More specifically, the surface layer of the photosensitive drum 1 (protective layer 1c in this embodiment) is composed mainly of acrylic resin. In this embodiment, as the resin (binding resin) constituting the protective layer 1c, an acrylic compound (monomer of acrylic resin) having an unsaturated bond and a methacrylic compound (monomer of methacrylic resin) crosslinked by using radiation such as ultraviolet rays or electron beams are used. Additives such as antioxidants, ultraviolet absorbing agents, plasticizers, fluorine atom-containing resin particles, and silicone compounds may be added to the protective layer 1c.

Each of the above layers can be formed by applying the coating liquid that constitutes each layer to the surface of the layer below the layer. When applying the coating liquid, for example, a dip coating method, a spray coating method, a spinner coating method, a roller coating method, a Mayer bar coating method, a blade coating method, or the like can be used.

3. Intermediate Transfer Belt Next, the intermediate transfer belt 8 will be described with reference to FIG.

In this embodiment, the intermediate transfer belt 8 has a base layer 8b and a surface layer 8a. In particular, in this embodiment, the intermediate transfer belt 8 is composed of two layers: the base layer 8b and the surface layer 8a formed on the base layer 8b. The surface layer 8a is a layer provided closer to the outer peripheral surface of the intermediate transfer belt 8 than the base layer 8b, and has a surface that carries (holds) the toner transferred from the photosensitive drum 1.

Materials constituting the base layer 8b include, for example, thermoplastic resins such as polycarbonate, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polymethylpentene-1, polystyrene, polyamide, polysulfone, polyarylate, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polyphenylene sulfide, polyethersulfone, polyethernitrile, thermoplastic polyimide, polyetheretherketone, thermotropic liquid crystal polymer, and polyamic acid. Two or more of these may be mixed and used. The base layer 8b can be obtained by melt-kneading a conductive material or the like in these thermoplastic resins, and then molding the mixture using an appropriate molding method such as inflation molding, cylindrical extrusion molding, or injection stretch blow molding.

In this embodiment, the surface layer 8a of the intermediate transfer belt 8 contains an acrylic resin 81. More specifically, the surface layer 8a of the intermediate transfer belt 8 is mainly composed of acrylic resin. The resin constituting the surface layer 8a is a curable material that is cured by irradiation with heat or energy rays such as light (ultraviolet rays, etc.) or electron beams, and is preferably an acrylic resin obtained by curing an acrylic copolymer containing unsaturated double bonds. As an acrylic copolymer containing unsaturated double bonds, for example, an acrylic ultraviolet curable resin: Opstar Z7501 manufactured by JSR Corporation can be used. In other words, the intermediate transfer belt 8 has a surface layer (cured film) 8a obtained by irradiating an energy ray to a liquid containing an ultraviolet curable monomer and/or oligomer component and curing it.

In this embodiment, a conductive material (conductive filler, electrical resistance adjuster) 82 is added to the surface layer 8a to adjust the electrical resistance. An electronically conductive material or an ionic conductive material can be used as the conductive material 82. Examples of the electronically conductive material include particulate, fibrous, or flaky carbon-based conductive fillers such as carbon black, PAN-based carbon fiber, and expanded graphite pulverized products. Examples of the electronically conductive material include particulate, fibrous, or flaky metal-based conductive fillers such as silver, nickel, copper, zinc, aluminum, stainless steel, and iron. Examples of the electronically conductive material include particulate metal oxide-based conductive fillers such as zinc antimonate, antimony-doped tin oxide, antimony-doped zinc oxide, tin-doped indium oxide, and aluminum-doped zinc oxide. Examples of the ionic conductive material include ionic liquids, conductive oligomers, and quaternary ammonium salts. One or more of these conductive materials can be appropriately selected and used, and an electronically conductive material and an ionically conductive material may be mixed and used. Among these, particulate (submicron or smaller particles, etc.) metal oxide-based conductive fillers are preferred because they can be added in small amounts.

In this embodiment, surface layer particles 83 are added to the surface layer 8a for the purpose of improving transfer efficiency and reducing friction with the belt cleaning blade 21. The surface layer particles 83 are preferably solid lubricants, and are usually insulating particles. The surface layer particles 83 may be, for example, one or more of fluorine-containing particles such as polytetrafluoroethylene (PTFE) resin powder, trifluorochloroethylene resin powder, tetrafluoroethylene hexafluoropropylene resin powder, vinyl fluoride resin powder, vinylidene fluoride resin powder, difluorodichloroethylene resin powder, and graphite fluoride, and copolymers thereof. The surface layer particles 83 may also be solid lubricants such as silicone resin particles, silica particles, and molybdenum disulfide powder. Among these, polytetrafluoroethylene (PTFE) resin particles (such as emulsion polymerization-based PTFE resin particles) are preferred because the friction coefficient of the particle surface is low and wear on other members that come into contact with the surface of the intermediate transfer belt 8, such as the belt cleaning blade 21, can be reduced.

An example of a method for producing the surface layer 8a is outlined below. Zinc antimonate particles as a conductive material and PTFE particles as a solid lubricant are mixed into an unsaturated double bond-containing acrylic copolymer, and the mixture is dispersed and mixed using a high-pressure emulsifier to produce a coating liquid for forming the surface layer. Methods for forming the surface layer 8a on the base layer 8b using this coating liquid for forming the surface layer include ordinary coating methods such as dip coating, spray coating, roll coating, and spin coating. By appropriately selecting and using one of these methods, the surface layer 8a can be obtained with the desired thickness.

The intermediate transfer belt 8 thus obtained preferably has a volume resistivity in the range of 10 ⁹ to 10 ¹² Ω·cm in terms of forming a good image. The volume resistivity was measured using a general-purpose measuring instrument Hiresta-UPMCP-HT450 (manufactured by Mitsubishi Chemical Corporation) in an environment at a temperature of 23.5° C. and a relative humidity of 60%.

4. Peripheral speed difference between the photosensitive drum and the intermediate transfer belt In this embodiment, a speed difference (peripheral speed difference) is provided between the peripheral speed of the photosensitive drum 1 and the peripheral speed of the intermediate transfer belt 8 in order to improve the primary transferability. In this embodiment, the peripheral speed difference is provided by making the peripheral speed of the photosensitive drum 1 smaller than the peripheral speed of the intermediate transfer belt 8. However, according to the study by the present inventor, it was found that the effect of improving the primary transferability does not change significantly even if the peripheral speed is reversed. In order to perform a good primary transfer of the toner image, this peripheral speed difference ({(peripheral speed of the intermediate transfer belt-peripheral speed of the photosensitive drum)/peripheral speed of the intermediate transfer belt}×100[%]) is at most 10% or less, preferably 5% or less, and more preferably 3% or less. In this embodiment, the peripheral speed difference is set to 1.5%, and the peripheral speed of the intermediate transfer belt 8 is set to 210 mm/sec while the peripheral speed of the photosensitive drum 1 is set to 206.85 mm/sec. In this embodiment, the peripheral speed of the photosensitive drum 1 is slower than that of the intermediate transfer belt 8, but the same effect can be obtained even if the peripheral speed of the photosensitive drum 1 is faster than that of the intermediate transfer belt 8.

5. Measurement of Tackiness Next, a description will be given of the measurement of the tackiness between the photosensitive drum 1 and the intermediate transfer belt 8. Fig. 4 is a schematic cross-sectional view of a measuring device for surface torque, which represents the tackiness between the photosensitive drum 1 and the intermediate transfer belt 8.

The photosensitive drum 1 and intermediate transfer belt 8 are left for at least 4 hours in an environment of temperature 23±3°C/humidity 50±5%. As shown in FIG. 4, the intermediate transfer belt 8 is triaxially stretched with a load of 29.4 N by three rollers, the jig drive roller 70, the jig tension roller 71, and the jig tension roller 72. The outer diameters of the jig drive roller 70, the jig tension roller 71, and the jig tension roller 72 are each 50 mm. The photosensitive drum 1 is abutted against the backup roller 73 with a force of 7.84 N, sandwiching the intermediate transfer belt 8 between them. The backup roller 73 is constructed with a rubber layer formed around a core metal, with a core metal diameter of 6 mm, a rubber diameter of 14 mm, and a rubber hardness of 20° Asker C. The jig drive roller 70 is driven by an Oriental Motor brushless motor (BLM5120HP-GFV) using a circuit (Oriental Motor, BMUD120-A2). The torque value is read using a unipulse digital indicator (F340A).

Specifically, the intermediate transfer belt 8 is accelerated uniformly from a stopped state to 180 mm/sec in 3.37 seconds, and the axial torque value of the jig drive roller 70 is sampled during this time. The sampling period is 10 msec. The sampled data for 2 seconds from the start of rotation is averaged. The above measurement is performed twice, and the average of each value is taken as the surface torque (N·m) that represents the tackiness of the intermediate transfer belt 8 and the photosensitive drum 1. The photosensitive drum 1 is fixed so that it does not rotate and is in a phase where the unused side abuts against the intermediate transfer belt 8 during measurement.

In this embodiment, the surface torque value is preferably in the range of more than 0.1 N·m and less than 0.5 N·m. When the surface torque value is 0.1 N·m or less, the level of exposure blur is so slight that it is not visible on the image, so there is little need to perform the operation of forming a lubricating toner image in the non-image portion, as is performed in this embodiment. In addition, when the surface torque value is 0.5 N·m or more, the motors that drive the photosensitive drum 1 and intermediate transfer belt 8 become larger and more expensive, which is not preferable.

6. Toner image for lubrication As described above, when there is a speed difference (peripheral speed difference) between the peripheral speed of the photosensitive drum 1 and the peripheral speed of the intermediate transfer belt 8, a frictional force is generated based on the difference in the friction coefficient between the two. The frictional force changes depending on whether or not there is a toner functioning as a lubricant between the photosensitive drum 1 and the intermediate transfer belt 8, and the rotation speed of the photosensitive drum 1 fluctuates. This causes the image exposure on the photosensitive drum 1 to be blurred, and a streaky image defect (exposure blur) may occur at the leading edge of the image. This exposure blur is likely to occur when there is a sudden change from a state where there is no toner between the photosensitive drum 1 and the intermediate transfer belt 8 to a state where there is toner. In other words, exposure blur is likely to occur when the area on the intermediate transfer belt 8 entering the primary transfer portion N1 changes from a non-image area to an image area. Typically, exposure blur is likely to occur when the area on the intermediate transfer belt 8 entering the primary transfer portion N1 changes from a non-image area downstream (leading edge) in the moving direction of the surface of the intermediate transfer belt 8 to the image area set for each sheet of transfer material S.

In this embodiment, the control unit 80 is configured to be able to perform control as follows. That is, the control unit 80 performs control so that a toner image of a print image to be secondarily transferred to the transfer material S based on image information is formed in an image portion on the intermediate transfer belt 8. At the same time, the control unit 80 performs control so that a lubricating toner image is formed in a non-image portion on the intermediate transfer belt 8 where the toner image of the print image is not formed, downstream of the image portion where the toner image of the print image is formed in the moving direction of the surface of the intermediate transfer belt 8. That is, in this embodiment, the control unit 80 forms a lubricating toner image on the intermediate transfer belt 8, which is a predetermined toner image that exists between the photosensitive drum 1 and the intermediate transfer belt 8 and functions as a lubricant, before forming the toner image of the print image on the intermediate transfer belt 8.

The "toner image of the print image" is a toner image that is formed on the transfer material S in response to an instruction from an external device such as a personal computer to constitute a product to be output from the image forming apparatus 100. The "toner image for lubrication" may be formed by the same image forming process as the "toner image of the print image", but it is not desirable to form it on the transfer material S to constitute a product to be output from the image forming apparatus 100. The "toner image for lubrication" may be partially or entirely transferred to the transfer material S and output from the image forming apparatus 100 together with the "toner image of the print image", as described below, but it is not desirable to make it visible (it is desirable that it is not visible). Here, with regard to the arrangement of the toner image formed on the intermediate transfer belt 8 or the arrangement of the image forming section P, "upstream", "downstream", "leading edge" or "rear edge" refers to the moving direction of the surface of the intermediate transfer belt 8, even if not specified. Here, the "toner image of the print image" may be simply called the "print image". Here, the "toner image for lubrication" may be simply called the "lubrication image".

Here, as shown in FIG. 15(a), generally, for each print image formed on one transfer material S, a transfer material area SR, an image area GR, and a non-image area NR, each having a predetermined width in the main scanning direction and the sub-scanning direction, are set on the intermediate transfer belt 8. Here, the "main scanning direction" is the direction that intersects (in this embodiment, approximately perpendicular) with the moving direction of the surface of the intermediate transfer belt 8 (or the photosensitive drum 1), and corresponds to the direction in which the laser beam of the exposure device 3 is scanned. The "sub-scanning direction" is the moving direction of the surface of the intermediate transfer belt 8 (or the photosensitive drum 1), and corresponds to the direction that is approximately perpendicular to the main scanning direction. The "transfer material area SR" is the area on the intermediate transfer belt 8 (or the corresponding area on the photosensitive drum 1) that comes into contact with the transfer material S at the secondary transfer portion N2. The "image area GR" is the area on the intermediate transfer belt 8 (or the corresponding area on the photosensitive drum 1) where a print image can be formed. The "non-image area NR" is an area where no print image is formed, which is typically located outside the image area and within the transfer material area at both ends of the image area in the main scanning direction and at both ends of the image area in the sub-scanning direction. Specifically, the control unit 80 sets the transfer material area SR, image area GR, and non-image area NR by outputting, to the exposure device 3 or the like, a signal indicating the image writing timing in the main scanning direction (and the image writing end timing) and a signal indicating the image writing timing in the sub-scanning direction (and the image writing end timing) for each print image formed on one transfer material S according to the size of the transfer material S.

In this case, the control unit 80 typically performs control so as to form a lubricating image in a non-image area NR (area LR in the figure) in the transfer material area (image formable area) SR and downstream (leading edge side) of the image area GR, as shown in FIG. 15(a). However, the present invention is not limited to this. For example, as shown in FIG. 15(b), when the transfer material area SR and the image area GR are substantially the same (so-called borderless printing), the control unit 80 can perform control as follows. That is, the control can be performed so as to form a lubricating image in an area (area LR in the figure) on the intermediate transfer belt 8 adjacent to the image area GR and the transfer material area SR downstream (leading edge side). In this case, as described later, the lubricating image may be adjacent to the print image without a gap, or may be adjacent with a gap. The same applies when there is no non-image area (margin) at least on the leading edge side. 15C, the control unit 80 may perform control so as to form a lubricant image LT in an area on the intermediate transfer belt 8 adjacent to the print image PT downstream (leading end) of the print image PT in the image area GR. The lubricant image LT may be formed across the image area and non-image area. In this case, too, the lubricant image may be adjacent to the print image with no gap, or adjacent to the print image with a gap, as described later.

In other words, in this embodiment, the control unit 80 outputs a signal for forming a lubricant image before outputting a signal for forming a print image, so that the lubricant image is primarily transferred onto the intermediate transfer belt 8 before the print image is primarily transferred onto the intermediate transfer belt 8.

This lubricant image can be prevented from being transferred to the transfer material S by adjusting the timing of application of the secondary transfer bias to the secondary transfer roller 11. For example, as shown in Figures 15(a) and (b), when the lubricant image is formed outside the image area, the lubricant image can be prevented from being transferred to the transfer material S in this manner. However, as described below, when the lubricant image is formed with yellow toner that is difficult to see, for example, the lubricant image may be partially or entirely transferred to the transfer material S. For example, the lubricant image may be transferred to the transfer material S when the lubricant image is formed inside the image area as shown in Figure 15(c) or when the lubricant is formed outside the image area as shown in Figure 15(a).

For example, as shown in FIG. 15(a), a further explanation will be given of a case where a lubricating image is formed in a non-image area downstream (leading end side) of the image area. As described above, in this embodiment, a lubricating image is formed in advance on the intermediate transfer belt 8 before the print image formed on the photosensitive drum 1 is primarily transferred onto the intermediate transfer belt 8. As a result, from the time when the transfer material area enters the primary transfer portion N1, toner is present between the intermediate transfer belt 8 and the photosensitive drum 1. Therefore, it is possible to suppress the image area from entering the primary transfer portion N1 and suddenly changing from a state without toner to a state with toner. This makes it possible to mitigate fluctuations in the rotation speed of the photosensitive drum 1. As a result, it is possible to perform stable image formation and obtain print images of high quality.

Here, the lubricating image is formed before the print image is formed. Therefore, when the image forming apparatus 100 has multiple image forming units P, it is preferable to form the lubricating image in the upstream image forming unit P that first forms a toner image. In addition, since the lubricating image is not a print image to be transferred to the transfer material S and output, it is preferable to form it with yellow toner, which is less visible. In other words, when the image forming apparatus 100 has multiple image forming units P that form toner images of different colors, it is preferable to form the lubricating image in the image forming unit PY that forms a toner image with yellow toner. However, for example, when a lubricating image is formed in a non-image area as shown in FIG. 15(a) and the lubricating image is controlled so as not to be transferred to the transfer material S, the lubricating image may be formed with any color of toner. In addition, the lubricating image may be formed using toners of multiple colors, with or without overlapping.

The lubricating image can be formed adjacent to the print image downstream (tip side) so that there is no gap between the print image. However, the present invention is not limited to this. For example, as shown in FIG. 15(a), a lubricating image may be formed in a non-image area downstream (tip side) of the image area, and there may be a gap between the non-image area and the image area where the print image is actually formed. In addition, as described below, when adjusting the toner amount of the lubricating image based on the image information of the print image, the print image and the lubricating image may be formed at different positions in the main scanning direction. It can be said that forming the lubricating image in close contact with the print image as described above is desirable in terms of reducing the fluctuation of the friction force. However, it is sufficient that the lubricating image is present on the intermediate transfer belt 8 downstream (tip side) of the print image, such as in the non-image area in the transfer material area shown in FIG. 15(a). As a result, before the print image is primarily transferred onto the intermediate transfer belt 8, the toner is present between the intermediate transfer belt 8 and the photosensitive drum 1, so that the fluctuation of the friction force can be reduced. More specifically, it is preferable that at least a part of the lubricating image exists within a distance range corresponding to the distance from the exposure position to the primary transfer position in the rotation direction of the photosensitive drum 1 downstream (tip side) of the downstream end (tip) of the print image. This is because at least a part of the lubricating image exists at the primary transfer portion N1 between the start of exposure of the print image and the primary transfer of the print image, and at least a part of the exposure blur caused by the fluctuation of the friction force can be reduced. For example, when a lubricating image is formed in a non-image area downstream (tip side) of the image area as shown in FIG. 15(a), a continuous lubricating image can be formed over the entire non-image area in the sub-scanning direction. In addition, when a lubricating image is formed outside the transfer material area as shown in FIG. 15(b) or within the image area as shown in FIG. 15(c), the following can be done. That is, as described above, a continuous lubricating image can be formed in the sub-scanning direction at a distance equal to or greater than the distance corresponding to the distance from the exposure position to the primary transfer position in the rotation direction of the photosensitive drum 1 downstream (tip side) of the downstream end (tip) of the print image.

In this embodiment, a pattern is formed as the lubricant image, in which one or more dot-unit micro-area toner images (herein also referred to as "micro dots") are dispersed in the main scanning direction and sub-scanning direction. The method of forming the micro dot pattern is not limited to this, but a method such as that described in Patent Document 1 can be used. In other words, the image area is divided into dot areas of m dots in the main scanning direction and n dots in the sub-scanning direction, and a toner image is repeatedly formed in one or more dots in the dot area, thereby forming a micro dot pattern.

7. Amount of Toner in Lubricating Toner Image Next, a method for changing the amount of toner in a lubricating toner image (lubricating image) formed in a non-image portion based on image information will be described.

As mentioned above, in the conventional techniques for forming a lubricating image, the lubricating image is formed at a predetermined printing rate across the entire width of the image area in the main scanning direction. This poses the problem of a large consumption of toner to form the lubricating image. For example, when forming a lubricating image with toner of a specific color among multiple color toners, there is a problem of a large consumption of toner of the color to form the lubricating image.

In this embodiment, a pattern of microdots is formed with yellow toner as an example of a lubricating image. FIG. 5(a) shows an example of a pattern of microdots as a lubricating image in this embodiment. One square in FIG. 5(a) represents one pixel (42 μm×42 μm), and a microdot is formed at the corresponding position by setting the data of the pixel shown in black in FIG. 5(a) to FFh. In the image forming apparatus 100 of this embodiment, the image data has 256 gradations from 00h to FFh, and FFh corresponds to full laser illumination. The pattern of microdots shown in FIG. 5(a) is a pattern in which microdots of the same size are arranged at an angle of 45° to the main scanning direction, with the dot interval in the main scanning direction being 0.84 mm and the dot interval in the sub-scanning direction being 0.42 mm. The print rate of the image data of this microdot pattern is 0.5%. Here, "printing rate" refers to the ratio (image ratio) of the total image data of pixels in a unit area, assuming that the total image data of all pixels in the unit area is 100% when the image data is FFh. The printing rate correlates with the amount of toner per unit area of the toner image. Note that here, an image with a printing rate of 100% is also called a solid image. Also, halftone images can include images with a printing rate of more than 0% and less than 100%, but typically have a printing rate of around 30% to 80%.

Figure 6 is a graph showing an example of the results of investigating the correlation between the width of a print image in the main scanning direction and the rank of exposure blur. Exposure blur was visually confirmed and ranked from 0 (best) to 16 (worst). For the evaluation print image, an image was formed in the center of the image area in the main scanning direction, with a width in the main scanning direction varying between 50 mm and 200 mm. This evaluation print image was a halftone image with a printing rate of 50% of the image data, and was a rectangular image with two sides approximately parallel to the main scanning direction and two sides approximately parallel to the sub-scanning direction. As shown in Figure 6, according to the inventor's research, it was found that the level of exposure blur improved when the width of the print image in the main scanning direction was narrowed.

Therefore, when the width of the print image in the main scanning direction is narrow, the width of the lubricant image in the main scanning direction does not need to be the entire width of the image area in the main scanning direction. In other words, for example, as in Comparative Example 1 shown in Figure 14, when the width of the print image 90 (a halftone image with a printing rate of 50% of the image data) in the main scanning direction is narrow, the width of the lubricant image 91 in the main scanning direction does not need to be the entire width of the image area in the main scanning direction.

In this embodiment, the control unit 80 performs control so as to change the amount of toner in the lubricant image formed in the non-image area based on the image information of the print image. In particular, in this embodiment, the control unit 80 performs control so as to change the size of the area in which the lubricant image is formed based on the image information of the print image. In other words, the control unit 80 performs control so that the width of the lubricant image in the main scanning direction is smaller when the width of the print image in the main scanning direction is a second width smaller than the first width than when the width of the print image in the main scanning direction is a first width.

Here, the width of the print image in the main scanning direction is represented by the distance between both ends of the print image in the main scanning direction at the downstream (leading end) end of the print image. The distance between both ends may be the distance between both ends of the region in the main scanning direction when the print image is a continuous region such as the rectangular halftone image. In addition, the distance between both ends may be the distance between both ends in the main scanning direction in the region containing the multiple images when the print image is a plurality of isolated images (such as text images). This "region containing multiple images" is the region between both ends of the multiple images in the main scanning direction and the sub-scanning direction. For example, in the case of multiple text images, the "region containing multiple images" is the range surrounded by two straight lines along the sub-scanning direction that pass through the outermost pixels of the text images at both ends in the main scanning direction, and two straight lines along the main scanning direction that pass through the outermost pixels at both ends in the sub-scanning direction of the multiple text images. Alternatively, the distance between both ends may be the sum of the distance between both ends of the multiple images in the main scanning direction. The "area of the lubricating image (the toner image for lubrication)" is the area between both ends in the main scanning direction and the sub-scanning direction. For example, when the lubricating image is formed in a pattern of microdots as in this embodiment, the "area of the lubricating image" is the range surrounded by two straight lines along the sub-scanning direction that pass through the outermost microdots at both ends in the main scanning direction, and two straight lines along the main scanning direction that pass through the outermost microdots at both ends in the sub-scanning direction. In this embodiment, the area of the lubricating image is a rectangular area having two sides that are approximately parallel to the main scanning direction and two sides that are approximately parallel to the sub-scanning direction. In addition, the lubricating image of the concrete example shown in this embodiment and the embodiment described later is formed in a non-image area downstream (tip side) of the image area as shown in FIG. 15(a), and the print image is formed adjacent to the boundary between the non-image area and the image area with almost no gap. In this embodiment, the area where the lubricating image (the toner image for lubrication) is formed, such as the area where the pattern of microdots is formed, is also simply called the "lubricating image".

Figure 7 is a schematic diagram of an example of a lubrication image formed according to this embodiment. In the example shown in Figure 7, the width of the print image 90 (a halftone image with a printing rate of 50% of the image data) in the main scanning direction is narrower than the width of the image area in the main scanning direction. In this case, in this embodiment, the control unit 80 sets the width of the lubrication image 92 to match the width of the print image 90 so that the width of the lubrication image 92 in the main scanning direction is the same as the width of the print image 90.

In the example of FIG. 7, the width of the lubricant image 92 in the main scanning direction is the same as the width of the printed image 90, but it is not necessary that they are exactly the same width. For example, as shown in FIG. 8, the width of the lubricant image 92a in the main scanning direction may be wider than the width of the printed image 90. Also, for example, as shown in FIG. 9, the width of the lubricant image 92b in the main scanning direction may be narrower than the width of the printed image 90. The width may be adjusted to an optimum value so as to suppress exposure blurring in accordance with the configuration of the image forming device 100, etc.

Also, as shown in Figs. 7 to 9, the control unit 80 can perform control to form the lubricant image so that at least a part of the lubricant image and at least a part of the print image overlap in the main scanning direction. However, the present invention is not limited to this. For example, as shown in Fig. 10, the position of the print image 90 and the positions of the lubricant images 92c and 92d may be separated in the main scanning direction. In the example of Fig. 10, two divided lubricant images are formed at positions different from the print image in the main scanning direction. In other words, the control unit 80 can perform control to form the lubricant image so that the lubricant image and the print image do not overlap in the main scanning direction. However, in this case, the boundary area between the lubricant image and the non-image portion increases, and the lubricant image may become more visible. Therefore, as shown in Figs. 7 to 9, it is preferable to form the lubricant image near the print image (at a position where at least a part of the lubricant image and at least a part of the print image overlap in the main scanning direction). In addition, if the lubrication image is made up of multiple divided parts as shown in FIG. 10, the total width of the widths of each part can be set according to the width of the print image (if the print image is made up of multiple isolated parts, this may be the total width of each part).

As described above, in this embodiment, the amount of toner in the lubricant image formed in the non-image area is changed based on the image information of the print image. This makes it possible to suppress the occurrence of exposure blur while suppressing the consumption of toner in forming the lubricant image.

[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.

In this embodiment, the printing rate of the lubricant image is changed based on the image information of the print image.

When the density of the print image is high, the exposure blur tends to be difficult to visually recognize on the image. Therefore, when the density of the print image is relatively high, the printing rate of the image data of the microdot pattern as the lubricant image can be lower than when the density of the print image is relatively low. Therefore, in this embodiment, the control unit 80 controls so that the printing rate of the lubricant image is smaller when the density of the print image is a second density higher than the first density than when the density of the print image is a first density. Typically, in this embodiment, the control unit 80 controls so that the printing rate of the lubricant image is smaller when the print image is a solid image than when the print image is a halftone image. The density of the print image can be expressed by the toner amount per unit area (mg/cm ² ) or the printing rate, and when the density is relatively high, the toner amount per unit area is larger and the printing rate is higher than when the density is relatively low.

Figure 11 is a schematic diagram of an example of a lubrication image formed according to this embodiment. The print image 90a shown in Figure 11 is a so-called solid image with a printing rate of 100% of the image data. In this case, exposure blurring is less noticeable than in the case of print image 90, which is a halftone image with a printing rate of 50% of the image data in the example described in Example 1 with reference to Figure 7. Therefore, in this case, even if the printing rate of the image data of the microdot pattern as the lubrication image 92e is 0.25%, half the 0.5% in Example 1, the occurrence of exposure blurring can be suppressed.

In addition, exposure blur tends to be less visible on the image when the printed image is a text image than when the printed image is a halftone image. Therefore, in this embodiment, the control unit 80 performs control so that the printing rate of the lubricant image is smaller when the printed image is a text image than when the printed image is a halftone image.

Figure 12 is a schematic diagram of another example of a lubrication image formed according to this embodiment. The print image 90b shown in Figure 12 is a text image. In this case, exposure blur is less noticeable than in the case of the print image 90, which is a halftone image in the example described in Example 1 with reference to Figure 7. Therefore, in this case, even if the printing rate of the image data of the microdot pattern as the lubrication image 92e is 0.25%, half of the 0.5% in Example 1, the occurrence of exposure blur can be suppressed. As the character size of the text becomes smaller, exposure blur becomes even less noticeable, so it is possible to further reduce the printing rate of the lubrication image.

As described above, in this embodiment, the printing rate of the lubricant image formed in the non-image area is changed based on image information. This makes it possible to further reduce the consumption of toner used to form the lubricant image while also suppressing the occurrence of exposure blur.

In addition, as in this embodiment, from the viewpoint of reducing the amount of toner consumed to form the lubricant image, it is preferable to change the size and printing rate of the lubricant image based on the image information of the print image, but it is also possible to change only the printing rate.

[Example 3]
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.

In this embodiment, the printing rate of the lubricant image is changed within the lubricant image area based on the image information of the print image.

In the first embodiment, the width of the lubricant image is narrowed according to the width of the print image, as shown in FIG. 7, for example. In this case, the boundaries between the lubricant image in the main scanning direction and the non-image areas (solid white areas) on both ends of the lubricant image may be more noticeable depending on the conditions. Therefore, in this embodiment, the control unit 80 performs control to change the printing rate of the lubricant image in the area where the lubricant image is formed based on the image information of the print image. More specifically, the control unit 80 sets the width of the lubricant image in the main scanning direction according to the width of the print image in the main scanning direction, and performs control so that the printing rate of the second part of the lubricant image on the end side in the main scanning direction is smaller than the printing rate of the first part of the lubricant image in the center in the main scanning direction.

Figure 13 is a schematic diagram of an example of a lubrication image formed according to this embodiment. In this example, the width of the lubrication image 93 (the same as the width of the print image 90c) is set to match the width of the print image 90c (a halftone image with a print rate of 50% of the image data) in the main scanning direction, and the print rate of the lubrication image is changed within the area of the lubrication image 93. Specifically, the print rate of the first part 93d in the center in the main scanning direction of the lubrication image 93 is set to 0.5%. In addition, the print rates of the second parts 93c and 93e adjacent to both sides of the first part 93d in the main scanning direction are set to 0.4%. In addition, the print rates of the third parts 93b and 93f adjacent to the outside of the second parts 93c and 93e in the main scanning direction are set to 0.3%. In addition, the print rates of the fourth parts (outermost parts) 93a and 93g adjacent to the outside of the third parts 93b and 93f in the main scanning direction are set to 0.2%. Thus, in the example of FIG. 13, a gradient is provided in the printing rate of the lubricant image so that the density of the lubricant image becomes thinner from the inside toward both ends in the main scanning direction within the lubricant image area. This makes the boundary between the lubricant image area and the solid white area less noticeable. In this way, the configuration of this embodiment can be said to be a more preferable configuration from the viewpoint of making the lubricant image less visible.

As described above, in this embodiment, the printing rate of the lubricant image is changed within the area of the lubricant image based on the image information. This makes it possible to reduce the amount of toner consumed to form the lubricant image, while making the boundary between the area of the lubricant image and the solid white area less noticeable and suppressing the occurrence of exposure blur.

[Example 4]
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.

In this embodiment, the control unit 80 controls the lubricating image so that the amount of toner on the trailing end side in the sub-scanning direction is greater than the amount of toner on the leading end side in the sub-scanning direction. That is, in this embodiment, the control unit 80 controls the amount of toner in the lubricating toner image in the first region close to the image portion in the non-image portion in the sub-scanning direction to be greater than the amount of toner in the lubricating toner image in the second region farther from the image portion in the non-image portion than the first region. In particular, in this embodiment, the control unit 80 controls the width of the lubricating toner image in the second region in the main scanning direction to be narrower than the width of the lubricating toner image in the first region.

Next, the amount of toner on the leading edge side in the sub-scanning direction of the lubricating image formed in the non-image portion will be described. As mentioned above, in the conventional technology for forming a lubricating image, the lubricating image is formed at a predetermined printing rate over the entire width of the image area in the main scanning direction. Therefore, as in the case of the above-mentioned printed image, the sudden change in frictional force from a state without toner to a state with toner may cause exposure blurring due to the lubricating image. If the length of the lubricating image in the sub-scanning direction can be set longer than the "distance corresponding to the distance from the exposure position to the primary transfer position in the rotation direction of the photosensitive drum 1", the above-mentioned exposure blurring due to the lubricating image is less noticeable. However, from the viewpoint of miniaturization of recent devices and minimizing the time from sending a print job to printing the first sheet, it is not preferable to make the length of the lubricating image longer than necessary.

Figure 16(a) is a schematic diagram of an example of a lubricant image formed according to this embodiment. In this embodiment, as shown in Figure 16(a), the formation of the lubricant image LR is controlled by the control unit 80 so that the amount of toner on the trailing end side in the sub-scanning direction is greater than the amount of toner on the leading end side in the sub-scanning direction. Figure 16(a) is an example of a case where a lubricant image LR is formed in the transfer material area SR. By forming a lubricant image such as that shown in Figure 16(a), it is possible to suppress the above-mentioned sudden change in frictional force and suppress exposure blur caused by the lubricant image. Figure 16(b) is an example of a case where a lubricant image LR4 according to this embodiment is formed in an area on the intermediate transfer belt 8 adjacent to the downstream side (leading end side) of the transfer material area SR, for example, during the above-mentioned borderless printing.

In this embodiment, a pattern of microdots is formed with yellow toner as an example of a lubricating image. FIG. 5(a) shows an example of a pattern of microdots as a lubricating image in this embodiment. One square in FIG. 5(a) represents one pixel (42 μm×42 μm), and a microdot is formed at the corresponding position by setting the data of the pixel shown in black in FIG. 5(a) to FFh. In the image forming apparatus 100 of this embodiment, the image data has 256 gradations from 00h to FFh, and FFh corresponds to full laser illumination. The pattern of microdots shown in FIG. 5(a) is a pattern in which microdots of the same size are arranged at an angle of 45° to the main scanning direction, with the dot interval in the main scanning direction being 0.84 mm and the dot interval in the sub-scanning direction being 0.42 mm. The print rate of the image data of this microdot pattern is 0.5%. Here, the "printing rate" is the ratio (image ratio) of the total image data of pixels in a unit area when the image data of all pixels in the unit area is FFh, assuming that the total image data is 100%. The printing rate correlates with the amount of toner per unit area of the toner image. Note that here, an image with a printing rate of 100% is also called a solid image. Also, a halftone image may include an image with a printing rate of more than 0% and less than 100%, but is typically an image with a printing rate of about 30% to 80%. Note that, as a guideline for the minimum amount of toner required to obtain the above-mentioned friction reduction effect, it is preferable that at least a portion of the lubricant image formed by microdots with a printing rate of 0.5% in the sub-scanning direction exists over the entire width of the image area GR in the main scanning direction.

Figure 5(b) shows an example of a more detailed arrangement of a microdot pattern in this embodiment, with the unit lattice being the above-mentioned "dot spacing of 0.84 mm in the main scanning direction and 0.42 mm in the sub-scanning direction." As shown in Figure 5(b), one unit lattice is arranged at the leading end in the sub-scanning direction, and by increasing the number of unit lattices in the main scanning direction by two as it approaches the trailing end in the sub-scanning direction, a lubrication image such as that shown in Figure 16(a) can be formed.

The setting of the toner amount at the leading end of the lubricant image in the sub-scanning direction will be further described with reference to the lubricant image LR5 shown in FIG. 16(c). The maximum toner amount at the leading end of the lubricant image in the sub-scanning direction required to suppress the exposure blur caused by the lubricant image described above is the toner amount when a lubricant image of about L3=100 mm shown in FIG. 16(c) is formed at the printing rate of the microdots in FIG. 5(a). L3 is the length in the main scanning direction of the lubricant image LR5 at the leading end in the sub-scanning direction. If this toner amount is the toner amount when a lubricant image with L3>100 mm is formed at the above printing rate, the friction force changes suddenly from a state without toner to a state with toner, so there is a possibility of exposure blur caused by the lubricant. Note that L1 in FIG. 16(c) is 200 mm, and L2 is 36 mm. L1 is the length in the main scanning direction of the lubricant image LR5 at the rear end in the sub-scanning direction. Also, L2 is the length in the sub-scanning direction of the lubricant image LR5.

In the example shown in FIG. 16(a), the lubrication image LR is formed by starting writing from the center in the main scanning direction and gradually expanding toward both ends in the main scanning direction as it moves toward the rear end in the sub-scanning direction. FIG. 17(a) is a schematic diagram of another example of a lubrication image formed according to this embodiment. In the example shown in FIG. 17(a), the lubrication image LR6 is formed by starting writing from both ends in the main scanning direction and gradually expanding toward the center in the main scanning direction as it moves toward the rear end in the sub-scanning direction. FIG. 17(b) is a schematic diagram of yet another example of a lubrication image formed according to this embodiment. In the example shown in FIG. 17(b), the lubrication image LR7 is formed by starting writing from any three positions in the main scanning direction and gradually expanding the width in the main scanning direction as it moves toward the rear end in the sub-scanning direction. In this way, the start of writing the lubrication image is not limited to the center in the main scanning direction as shown in FIG. 16(a), and the same effect can be obtained even if it is shown in FIG. 17(a) or (b).

As described above, in this embodiment, the amount of toner on the trailing end side of the lubricant image in the sub-scanning direction is controlled to be greater than the amount of toner on the leading end side. This makes it possible to suppress exposure blur caused by the lubricant toner image while also suppressing the occurrence of exposure blur caused by the print image.

[Example 5]
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.

In this embodiment, the control unit 80 controls the lubricating image so that the density at the leading end in the sub-scanning direction is lighter than the density at the trailing end. In other words, in this embodiment, similar to the fourth embodiment, the control unit 80 controls the amount of toner in the lubricating toner image in the first region close to the image portion in the non-image portion in the sub-scanning direction to be greater than the amount of toner in the lubricating toner image in the second region farther from the image portion in the non-image portion than the first region. In particular, in this embodiment, the control unit 80 controls the density of the lubricating toner image in the second region to be less than the density of the lubricating toner image in the first region.

Figure 18 is a schematic diagram of an example of a lubricant image formed according to this embodiment. In this embodiment, the control unit 80 controls to form lubricant images LR1, LR2, and LR3 with different densities on the tip side of the image area GR. The lubricant image LR1 closest to the image area GR is a lubricant image made of minute dots shown in Figure 5 (a) described in Example 1, and has a printing rate of 0.5%. The printing rate of the lubricant image LR2 adjacent to the lubricant image R1 on the tip side of the lubricant image LR1 is 0.25%, which is half the printing rate of the lubricant image LR1 and has a low density. Furthermore, the printing rate of the lubricant image LR3 adjacent to the lubricant image LR2 on the tip side of the lubricant image LR2 is 0.125%, which is set to a quarter of the density of the lubricant image LR1. By reducing the density of the lubricant image on the tip side in the sub-scanning direction in this way, the occurrence of exposure blur caused by the lubricant image described above can be suppressed.

The maximum printing rate at the leading end of the lubricant image in the sub-scanning direction required to suppress exposure blur caused by the lubricant image described above is approximately 0.25%. If this printing rate exceeds 0.25%, the frictional force changes suddenly from a state without toner to a state with toner, and exposure blur caused by the lubricant may occur. Note that the toner amount corresponding to this printing rate of 0.25% corresponds to the toner amount when the microdots with a printing rate of 0.5% shown in Figure 5(a) described in Example 1 are formed in the area of L3 = 100 mm shown in Figure 16(c).

As described above, in this embodiment, the density of the leading end of the lubricant image in the sub-scanning direction is controlled to be lighter than the density of the trailing end. This makes it possible to suppress exposure blur caused by the lubricant toner image while also suppressing the occurrence of exposure blur caused by the print image.

[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.

In the above embodiment, the lubricating image is formed using yellow toner, but the present invention is not limited to this. For example, an image forming unit that forms a toner image using transparent toner may be provided in the image forming device, and the lubricating image may be formed using transparent toner by this image forming unit. The configuration and operation of the image forming unit that forms the toner image with transparent toner can be the same as in the above embodiment. This makes the lubricating image more difficult to see. Also, when forming a lubricating image with transparent toner, it is preferable that the image forming unit that forms the toner image with the transparent toner is located at the most upstream of the multiple image forming units.

Moreover, the lubricant image, which is present between the image carrier and the intermediate transfer body and functions as a lubricant, including the toner image for lubrication formed in a pattern of minute dots, is not limited to being formed with toner. For example, the lubricant image may be formed with an external additive of toner such as zinc stearate, graphite fluoride such as Sefbon (manufactured by Central Glass Co., Ltd.), or silicone resin fine particles such as Tospearl (manufactured by Nippon Shokugyo Co., Ltd.). That is, the image forming apparatus may have a lubricant image forming section that forms a lubricant image on the surface of the intermediate transfer body, and a control section that controls the image forming section to form a toner image of a print image based on image information in the image section on the intermediate transfer body, and the lubricant image forming section to form a lubricant image in a non-image section on the intermediate transfer body where a toner image of a print image is not formed, downstream of the image section in the moving direction of the surface of the intermediate transfer body. The control section can control to change the amount of lubricant in the lubricant image formed in the non-image section based on the image information of the print image.

In the above embodiment, a pattern of minute dots as a digital halftone formed by fully lighting the laser based on predetermined image data has been described as an example of a lubricant image, but the present invention is not limited to this. For example, a similar effect can be obtained with an analog halftone such as a so-called fog toner. An analog halftone is a halftone image formed by moving toner from a developer carrier onto an image carrier in accordance with the potential difference between the surface of the image carrier and a developer carrier to which a predetermined development bias is applied. For example, after charging the image carrier, the entire surface of the image carrier is partially exposed with an appropriate amount of exposure light, making it easier for the toner to transfer to parts of the surface of the image carrier, and an analog halftone can be formed at a desired position in the main scanning direction as in the above embodiment. Note that the lubricant image made of the above-mentioned example lubricant can be formed by transferring these lubricants, which are charged with a polarity opposite to that of the toner, to the image carrier in a manner to form the analog halftone, and then transferring them to an intermediate transfer body by appropriately controlling the primary transfer bias.

In the above embodiment, the present invention is applied to an image forming apparatus having multiple image forming units, but the present invention is not limited to this. For example, the present invention can also be applied to an image forming apparatus having only one image forming unit, such as a monochrome image forming apparatus. In this case, the lubricant image is formed in the image forming unit that forms the print image.

In addition, in the above-described embodiment, a peripheral speed difference was intentionally provided between the image carrier and the intermediate transfer body. Even in a configuration in which a peripheral speed difference is not intentionally provided in this way, a peripheral speed difference may occur unintentionally due to eccentricity of the drive roller, etc. Even in such an image forming device, by applying the present invention, it is possible to suppress exposure blur caused by fluctuations in the rotation speed of the image carrier due to the presence or absence of toner in the primary transfer section.

REFERENCE SIGNS LIST 1 Photosensitive drum 2 Charging roller 3 Exposure device 4 Developing device 5 Primary transfer roller 6 Drum cleaning device 8 Intermediate transfer belt

Claims (18)

In an image forming apparatus for forming a toner image on a recording material,
an image forming unit that forms the toner image on an image carrier;
an intermediate transfer body which is movable to form a primary transfer portion in contact with the image carrier, and which forms an image portion in an image formable area of a recording material corresponding to an area where the toner image can be formed by a first toner image which is the toner image primarily transferred from the image carrier at the primary transfer portion;
a control unit that performs control so as to form a second toner image, which is a toner image for lubrication, in a non-image portion , which is a region in the image formable region of the intermediate transfer body where the first toner image of a print image based on image information is not formed,
the control unit performs control so that the second toner image is not formed in a region of the intermediate transfer body where the image portion is formed and in a region of the non-image portion that overlaps with the region where the image portion is formed when viewed in a width direction of the intermediate transfer body perpendicular to the moving direction of the surface of the intermediate transfer body, and performs control so that the second toner image is formed in the first non-image portion in a state in which a first non-image portion, which is the non-image portion, is formed downstream of the image portion with respect to the moving direction of the surface of the intermediate transfer body;
The control unit performs control to change the size of the area in which the second toner image is formed based on the image information, and performs control so that, in the width direction, the second toner image formed in the first non-image area has the same width as the width of the first toner image formed in the image area or has a width that is located more inward than the first toner image, and is not formed more outward than the first toner image. The image forming apparatus according to claim 1, characterized in that there is a speed difference between the moving speed of the surface of the image carrier and the moving speed of the surface of the intermediate transfer body. The image forming apparatus according to claim 1 or 2, characterized in that the value of the surface torque representing the tackiness between the image carrier and the intermediate transfer body is greater than 0.1 N·m and less than 0.5 N·m. The image forming apparatus according to any one of claims 1 to 3, characterized in that the control unit performs control so that the width of the second toner image in the width direction of the print image is smaller when the width of the first toner image in the width direction is a first width than when the width of the second toner image in the width direction is a second width smaller than the first width. The image forming device according to any one of claims 1 to 4, characterized in that the control unit performs control to change the printing rate of the second toner image based on the image information. The image forming device according to claim 5, characterized in that the control unit performs control so that the printing rate of the second toner image is smaller when the density of the print image is a second density higher than the first density than when the density of the print image is a first density. The image forming device according to claim 5, characterized in that the control unit performs control so that the printing rate of the second toner image is smaller when the print image is a solid image than when the print image is a halftone image. The image forming device according to claim 5, characterized in that the control unit performs control so that the printing rate of the second toner image is smaller when the print image is a text image than when the print image is a halftone image. The image forming device according to any one of claims 1 to 8, characterized in that the control unit performs control so as to change the printing rate of the second toner image within the area where the second toner image is formed based on the image information. 10. The image forming apparatus according to claim 9, wherein the control unit sets the width of the second toner image in the width direction in accordance with the width of the first toner image of the print image in the width direction, and performs control so that the printing rate of the second portion of the second toner image on the end side in the width direction is smaller than the printing rate of the first portion of the second toner image in the center in the width direction. The image forming apparatus according to any one of claims 1 to 10, characterized in that it has a plurality of image forming units along the moving direction of the surface of the intermediate transfer body, and the second toner image is formed by at least one of the plurality of image forming units. The image forming apparatus according to claim 11, characterized in that the second toner image is formed in the image forming unit located most upstream in the direction of movement of the surface of the intermediate transfer body among the multiple image forming units. The image forming apparatus according to claim 11 or 12, characterized in that the image forming units each form the toner image of a different color, and the second toner image is formed by one of the image forming units that forms the toner image with yellow toner. The image forming apparatus according to claim 11 or 12, characterized in that the plurality of image forming units each form the toner image of a different color, and the second toner image is formed by one of the plurality of image forming units that forms the toner image with a transparent toner. the first toner image in the image portion that has been primarily transferred to the intermediate transfer body in the primary transfer section is transported by the intermediate transfer body, and the transported first toner image is secondarily transferred to a recording material in a secondary transfer section;
The image forming apparatus according to any one of claims 1 to 14, characterized in that the control unit controls the second toner image to be formed outside an image area in which the first toner image of the print image can be formed, in the transfer material area on the intermediate transfer body that contacts the transfer material at the secondary transfer unit. In an image forming apparatus for forming a toner image on a recording material,
an image forming unit that forms the toner image on an image carrier;
an intermediate transfer body which is movable to form a primary transfer portion in contact with the image carrier, and which forms an image portion in an image formable area of a recording material corresponding to an area where the toner image can be formed by a first toner image which is the toner image primarily transferred from the image carrier at the primary transfer portion;
a control unit that performs control so as to form a second toner image, which is a toner image for lubrication, in a non-image portion , which is a region in the image formable region of the intermediate transfer body where the first toner image of a print image based on image information is not formed,
the control unit performs control so that the second toner image is not formed in a region of the intermediate transfer body where the image portion is formed and in a region of the non-image portion that overlaps with the region where the image portion is formed when viewed in a width direction of the intermediate transfer body perpendicular to the moving direction of the surface of the intermediate transfer body, and performs control so that the second toner image is formed in the first non-image portion in a state in which a first non-image portion, which is the non-image portion, is formed downstream of the image portion with respect to the moving direction of the surface of the intermediate transfer body;
The control unit performs control in the direction of movement of the surface of the intermediate transfer body so that the amount of toner of the second toner image in a first region close to the image portion in the first non-image portion is greater than the amount of toner of the second toner image in a second region in the first non-image portion farther from the image portion than the first region, and performs control in the width direction so that the second toner image formed in the first non-image portion has the same width as the width of the first toner image formed in the image portion or has a width that is located more inward than the first toner image, and is not formed more outward than the first toner image . 17. The image forming apparatus according to claim 16, wherein the control unit performs control so that the width of the second toner image in the second region is narrower than the width of the second toner image in the first region in the width direction. 17. The image forming apparatus according to claim 16, wherein the control unit performs control such that a density of the second toner image in the second area is smaller than a density of the second toner image in the first area.

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