JP4250395B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine using an electrophotographic method, and more particularly, a plurality of color toner images formed on a plurality of image carriers are used as a transfer material on a transfer material conveying belt. The present invention relates to an image forming apparatus that sequentially transfers images on a transfer material, or sequentially superimposes them on an intermediate transfer belt for primary transfer, and then collectively transfers them to a transfer material to obtain a color image on the transfer material.
[0002]
[Prior art]
  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus is known that transfers a toner image formed on an image carrier using electrophotography onto a transfer material and obtains an image on the transfer material. Under these circumstances, with the progress of the information society in recent years, needs for color image forming apparatuses are widening. Furthermore, in order to increase the speed of color image output, a plurality of image carriers are arranged in a line, and a toner image is sequentially formed on each image carrier, and the toner images are directly transferred to a transfer material or via an intermediate transfer member. In-line image forming apparatuses that transfer images are attracting attention.
[0003]
  An example of an electrophotographic inline-type full-color image forming apparatus will be briefly described with reference to FIG. 1. The image forming apparatus has four color images of yellow (Y), magenta (M), cyan (C), and black (K). Forming units (image forming stations 10) 10Y, 10M, 10C, and 10K are provided, and each station has a photosensitive drum 70 (70Y to 70K) as an image carrier.
[0004]
  In order to form an image, first, the surface of the photosensitive drum 70 (70Y to 70K) of each station is uniformly charged by the primary charging roller 12 (12Y to 12K), and then the original is scanned by the laser exposure unit 13 (13Y to 13K). The image is subjected to color separation, and an electrostatic latent image corresponding to the separation color of the original is formed on the surface of the photosensitive drum 70, and the latent image is developed with minus toner by the developing device 14 (14Y to 14K). Then, a toner image of each color is formed on the surface of the photosensitive drum 70, and the toner image of each color on the photosensitive drum 70 is applied to the intermediate transfer belt 80 with a primary transfer power supply primary transfer voltage 48 (48Y). To 48K), the primary transfer roller 54 (54Y to 54K) as a transfer means to which a primary transfer voltage is applied is sequentially superposed and primarily transferred. Note that the transfer residual toner adhering to the surface of the photosensitive drum 70 after the transfer is removed by the drum cleaner 16 and used for the next image formation.
[0005]
  Thereafter, the four-color toner images on the intermediate transfer belt 80 are collectively put on the transfer material P conveyed to the intermediate transfer belt 80 by the secondary transfer roller 55 to which a secondary transfer voltage is applied from the secondary transfer power source 49. The transfer material P after the secondary transfer and the secondary transfer is completed is conveyed to the fixing device 40, and is pressurized and heated to melt and mix the four color toners and fixed on the transfer material P. Thus, the transfer material P is full color. An image is formed. On the other hand, the transfer residual toner remaining on the surface of the intermediate transfer belt 80 that has finished the secondary transfer is removed by the belt cleaner 33. In such an image forming apparatus, the direction in which the laser beam is scanned is referred to as a main scanning direction, and the direction in which the surface of the photosensitive drum 70 or the intermediate transfer belt 80 travels is referred to as a sub-scanning direction.
[0006]
  By the way, in the image forming apparatus provided with the conventional developing device 14 described above, as the total number of printed sheets using the developing device 14 increases, the deterioration of the toner is promoted, and the toner having a polarity opposite to that of the regular toner increases. To do. Then, the toner having the opposite polarity is transferred to the non-image portion on the photosensitive drum 70 (hereinafter, this phenomenon is referred to as reverse fog). This reversal fog is not easily transferred to the transfer material P and has little influence on the image. However, even if the toner has a normal polarity, if the amount of charged charge is low, the toner is thinly developed in the non-image area (hereinafter referred to as “reverse fog”). , Referred to as “fogging”), resulting in degradation of image quality.
[0007]
  For example, in recent years, especially in color machines, there are an increasing number of cases where glossy paper such as gloss paper is printed. In such cases, lowering the fixing speed of the device and increasing the glossiness of the image results in higher image quality. We are trying to make it. At this time, if there is fogging, even if it is not noticeable on plain paper, the toner fixability is improved on glossy paper, so that the area when the toner is crushed is large, and as a result, it becomes noticeable.
[0008]
  Further, since the glossy paper itself is a paper with high whiteness, fog is conspicuous. In addition, the weakly charged toner makes it easy to develop the toner on the periphery of the latent image, so that the line image and characters are thickened, and the image quality is deteriorated such as collapse of thin lines. Further, the weakly charged toner weakens the power of moving onto the intermediate transfer belt 80 or the transfer material P due to the transfer electric field during the primary transfer or the secondary transfer, resulting in a decrease in density of a solid image or the like due to transfer failure. These phenomena have a significant tendency after a pause in a high temperature and high humidity environment.
[0009]
  On the other hand, in the image forming apparatus provided with the conventional developing device 14 described above, the deterioration of the toner is promoted even when the continuous printing operation is continued for a long time. In this case, the toner is more strongly charged than the regular toner. Increased high tribo toner. Since the strongly charged toner has increased adhesion to each member, the developability onto the photosensitive drum 70 and the transfer property onto the intermediate transfer belt 80 and the transfer material P are deteriorated, and a solid image or the like is deteriorated. Causes a decrease in concentration. Further, the strongly charged toner increases the electrical repulsion between the toners, and therefore causes image quality degradation such as scattering during transfer of line drawings and characters. These tendencies are remarkable after continuous printing in a low temperature and low humidity environment.
[0010]
  As described above, various image defects caused by the developing device 14 occur, and as a result, it is difficult to always obtain a good print image. For this reason, conventionally, toner that has decreased or increased from the developing sleeve in the developing unit 14 and its vicinity is developed as a toner image such as a solid image on the photosensitive drum 70 at every predetermined timing other than during the printing operation. A so-called developing device adjustment mode is executed in various image forming apparatuses. By executing this mode, the toner tribo in the developing device 14 can be readjusted to a preferable charged charge amount, and printing can be performed. Therefore, various image defects caused by the developing device 14 can be prevented. It becomes possible. The toner images (adjustment toner images) discharged onto the photosensitive drums 70Y to 70K are sequentially transferred onto the intermediate transfer belt 80, and then conveyed to the belt cleaner 33 and removed.
[0011]
  When toner is discharged in the developer adjustment mode in the inline-type full-color image forming apparatus described above, for example, a first color (yellow Y) adjustment toner image is transferred onto the intermediate transfer belt 80 from the photosensitive drum 70Y. Until it is conveyed to the belt cleaner 33, the other three photosensitive drums 70M to 70K are brought into contact with each other. At this time, the toner image for adjustment on the intermediate transfer belt 80 comes into contact with each photoconductor drum 70, so that a part of the toner forming the toner image moves from the intermediate transfer belt 80 onto the photoconductor drum 70. So-called retransfer occurs.
[0012]
  In a normal printing operation, even if such re-transfer occurs in the first color toner image and a part of the toner image is transferred onto the second and subsequent photosensitive drums 70, the drum cleaner 16 Is completely removed. However, in the developing device adjustment mode, in order to efficiently discharge the toner in the developing device 14 to the outside of the developing device 14, a solid image over the entire main scanning direction (and a predetermined length in the sub scanning direction) of the image forming apparatus. The toner is discharged using the pattern or the like. Therefore, the total amount of toner retransferred at once onto the photosensitive drum 70 for the second and subsequent colors also increases, and all of the toner cannot be collected by the drum cleaner 16, and a part of the toner is on the surface of the photosensitive drum 70. May stay. Similarly, the toner images for adjustment of the second color (magenta M) and the third color (cyan C) are somewhat different, and the retransfer toner stays on the photosensitive drum 70 for the third and subsequent colors. Sometimes. These staying toners contaminate the surfaces of the photosensitive drum 70 and the primary charging roller 12 and cause new image defects such as image streaks and density unevenness in a halftone image portion or the like in subsequent printing.In addition, since the adjustment toner images for each color are sequentially transferred, if an operation for discharging the adjustment toner images is interrupted before the image formation is completed, an attempt to discharge a plurality of adjustment toner images will result in a normal image. It takes time to start forming.
[0013]
  Here, a supplementary explanation regarding the retransfer will be given. FIG. 2 shows the relationship between the primary transfer voltage, the transfer efficiency, and the retransfer rate in the image forming station of the conventional image forming apparatus.
[0014]
  The transfer efficiency indicates the ratio of the toner amount of the toner image transferred onto the intermediate transfer belt 80 to the total toner amount of the toner image developed on the photosensitive drum 70, and the retransfer rate indicates the intermediate transfer at a certain station. The ratio of the amount of toner that is reversely transferred to the photosensitive drum at the next downstream station with respect to the total toner amount of the toner image transferred onto the belt 80 is shown.
[0015]
  Within the range of the transfer voltage in the figure, the transfer efficiency and the retransfer rate both monotonically increase with respect to the transfer voltage. Therefore, in the present image forming apparatus, the transfer voltage at each station during the printing operation is set to 200 V, in which both high transfer efficiency and low retransfer rate are satisfactorily achieved. As a result, a full-color image with sufficient density for each color is output.
[0016]
  In the conventional developer adjustment mode, when the adjustment toner image is transferred from the photosensitive drum 70 onto the intermediate transfer belt 80, the adjustment toner image on the intermediate transfer belt 80 is transferred to another downstream photosensitive drum. The same primary transfer voltage was set at the time of contact with 70.
[0017]
[Problems to be solved by the invention]
  However, under the voltage setting as described above, retransfer occurs as described above, and a new image defect may occur in subsequent printing.
[0018]
  Therefore, the present invention prevents a new image defect from occurring after the toner is discharged from the image carrier.Even if the operation of discharging the adjustment toner image before the completion of the image formation is interrupted, a decrease in the image formation throughput is prevented.For the purpose.
[0019]
[Means for Solving the Problems]
  In order to achieve the above object, a typical configuration of the present invention is as follows.
  A plurality of photoreceptors each rotating in the sub-scanning direction;
  Exposure means for scanning the photoconductor in a main scanning direction to form an electrostatic latent image;
  A plurality of developing units that contain toner and supply toner to each photoconductor to form a toner image;
  Rotate in the sub-scanning directionAn intermediate transfer member;
  Cleaning means for removing toner adhering to the intermediate transfer member;
  EachPhotoconductorPlaced on top of each other,A plurality of transfer means for transferring a toner image onto the intermediate transfer member,
  The plurality of photosensitive members are arranged side by side in the rotation direction of the intermediate transfer member, and an adjustment toner image for discharging deteriorated toner from the plurality of developing devices is transferred onto the intermediate transfer member to adjust image quality. DoIn the image forming apparatus,
  Forming an adjustment toner image having a length in the sub-scanning direction shorter than a distance between transfer positions of the adjacent transfer units on each of the photoconductors by the developing units;
The plurality of adjustment toner images formed are transferred onto the intermediate transfer body almost simultaneously by the plurality of transfer means,
  At each transfer position of the plurality of transfer means,The upstream side of the rotation direction of the intermediate transfer memberWhen the adjustment toner image transferred by the transfer means passes through the transfer position,For the adjustment The toner image was transferred to the intermediate transfer member.It is characterized in that an electric field weaker than time is formed.
[0020]
  Or a plurality of photoreceptors each rotating in the sub-scanning direction;
  Exposure means for scanning the photoconductor in a main scanning direction to form an electrostatic latent image;
  A plurality of developing units that contain toner and supply toner to each photoconductor to form a toner image;
  A transfer material carrier that carries the transfer material and rotates in the sub-scanning direction;
  Cleaning means for removing toner adhering to the transfer member carrier;
  A plurality of transfer means arranged to face each of the photoconductors and transferring a toner image onto the transfer material,
  The plurality of photoconductors are arranged side by side in the rotation direction of the transfer material carrier, and an adjustment toner image for discharging deteriorated toner from the plurality of developing devices is transferred onto the transfer material carrier. In the image forming apparatus for adjusting the quality,
  Forming an adjustment toner image having a length in the sub-scanning direction shorter than a distance between transfer positions of the adjacent transfer units on each of the photoconductors by the developing units;
  The plurality of adjustment toner images formed are transferred onto the transfer material carrier almost simultaneously by the plurality of transfer means,
  At each transfer position of the plurality of transfer means, when the adjustment toner image transferred by the transfer means upstream of the transfer material carrier in the rotation direction passes through the transfer position, the adjustment toner image is A weaker electric field is formed than when the image is transferred to the transfer material carrier..
[0021]
DETAILED DESCRIPTION OF THE INVENTION
  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.
[0022]
  (Reference example 1)
  Figure 1,An image forming deviceReference exampleIt is a schematic block diagram which shows. This image forming apparatus is configured as a four-drum, intermediate transfer type full-color printer. As shown in FIG. 1, the image forming apparatus includes four color image forming units (image forming stations 10) 10Y, 10M, and 10C of yellow (Y), magenta (M), cyan (C), and black (K). And a transfer device including an intermediate transfer belt 80 as an intermediate transfer member, and a fixing device 40.
[0023]
  Each of the image forming stations 10Y, 10M, 10C, and 10K is configured as an image forming unit, and photosensitive drums (drum-shaped electrophotographic photosensitive members) 70Y, 70M, 70C, and 70K that are image carriers can rotate in the direction of arrow a. Is installed. Primary charging rollers 12Y, 12M, 12C, and 12K for uniformly charging the surface of the photosensitive drum are disposed on the outer peripheral surfaces of the photosensitive drums 70Y, 70M, 70C, and 70K, respectively. Further, laser exposure units 13Y, 13M, 13C, and 13K for exposing the surface of the photosensitive drum with laser light modulated in accordance with the image signal are further provided on the surface of the photosensitive drum formed by laser exposure on the downstream side. Developing units 14Y, 14M, 14C, and 14K that develop the electrostatic latent images of the respective colors using the corresponding yellow, magenta, cyan, and black toners are disposed.
[0024]
  Primary transfer rollers 54Y, 54M, 54C, and 54K that form a primary transfer portion together with the photosensitive drum are opposed to each other at a position (transfer position) between the photosensitive drums 70Y, 70M, 70C, and 70K with the intermediate transfer belt 80 interposed therebetween. ing. Primary transfer power supplies 48Y, 48M, 48C, and 48K are connected to the primary transfer rollers 54Y, 54M, 54C, and 54K as primary transfer power supplies, and variable primary transfer voltages Vy, Vm, Vc, and Vk are applied to the primary transfer rollers 54Y, 54M, 54C, and 54K, respectively. .
[0025]
  The intermediate transfer belt 80 is stretched and installed on three rollers, that is, a driving roller 51, a tension roller 52, and a secondary transfer counter roller 53. The intermediate transfer belt 80 passes through the image forming stations 10Y to 10K and passes through the photosensitive drums 70Y to 70Y. It is placed in contact with 70K. The intermediate transfer belt 80 is rotationally driven by the drive roller 51 in the direction of the arrow b in the figure. Drum cleaners 16Y, 16M, 16C, and 16K are installed downstream of the primary transfer rollers 54Y, 54M, 54C, and 54K of the photosensitive drums 70Y, 70M, 70C, and 70K. A belt cleaner 33 is disposed at the drive roller 51 of the intermediate transfer belt 80.
[0026]
  The image forming operation of the image forming apparatus configured as described above will be described using the yellow image forming station 10Y as an example. The photoconductive drum 70Y of the yellow station 10Y has a photoconductive layer formed on the surface of an aluminum cylinder, and the surface is uniformly negatively charged (charged) by the primary charging roller 12Y in the process of rotating in the direction of arrow a. Then, image exposure is performed by the laser exposure device 13Y (surface potential after exposure = -200V), and an electrostatic latent image corresponding to the yellow image component of the document is formed on the surface of the photosensitive drum 70Y. It is formed. This latent image is developed using negatively charged yellow toner by the developing device 14Y, and the latent image is visualized as a yellow toner image.
[0027]
  The obtained yellow toner image is primarily transferred onto the intermediate transfer belt 80 by applying a primary transfer voltage from the primary transfer power supply 48Y to the primary transfer roller 54Y. After the transfer, the transfer residual toner adhering to the surface of the photosensitive drum 70Y is removed by the drum cleaner 16Y and used for the next image formation.
[0028]
  The above-described image forming operation is performed at a predetermined timing in each of the image forming stations 10Y to 10K, and the toner images on the photosensitive drums 70Y to 70K are sequentially superimposed on the intermediate transfer belt 80 at the respective primary transfer portions to be primary. Transcript. In the full color mode, the toner images are sequentially transferred to the intermediate transfer belt 80 in the order of yellow, magenta, cyan, and black. In the single color or 2-3 color mode, the toner images of the necessary colors are as described above. Transcribed in the same order.
[0029]
  Thereafter, the four-color toner images on the intermediate transfer belt 80 are transferred to the secondary transfer counter roller in which the secondary transfer roller 55 is grounded with the intermediate transfer belt 8 interposed therebetween as the intermediate transfer belt 80 rotates in the direction of arrow b. The secondary transfer voltage from the secondary transfer power supply 49 to the secondary transfer roller 55 is transferred onto the transfer material P which is moved to the secondary transfer portion in contact with the roller 53 and supplied thereto at a predetermined timing by the feeding roller 20. The secondary transfer is performed collectively by applying.
[0030]
  The transfer material P on which the four-color toner images are secondarily transferred is conveyed to the fixing device 40, where it is pressurized and heated, and the four-color toners are melted and mixed to be fixed on the transfer material P. A full color image is formed. On the other hand, the transfer residual toner remaining on the surface of the intermediate transfer belt 80 that has finished the secondary transfer is removed by the belt cleaner 33.
[0031]
  BookReference exampleThen, a negatively chargeable OPC drum having a diameter of 30.6 mm is used for the photosensitive drum 70 (70Y to 70K), and a charging voltage in which an AC component is superimposed on a DC component is applied to the primary charging roller 12 (12Y to 12K). Regardless of the environment, the surface of the photosensitive drum 70 was uniformly charged to about -600V. The laser exposure device 13 (13Y to 13K) includes a near-infrared laser diode having a wavelength of 760 nm and a polygon mirror that scans the photosensitive drum 70 with laser light, and the surface potential of the photosensitive drum 70 is − The voltage is lowered to 200 V, and an electrostatic latent image having this as an image portion is formed.
[0032]
  The developing device 14 (14Y to 14K) is a jumping developing type developing device using a non-magnetic toner (non-magnetic one-component developer), and has a core / shell structure particle size of 6 μm containing a wax as the non-magnetic toner. Using toner, this is coated on the surface of the developing sleeve by the application roller and carried, and the thickness of the toner layer is regulated by an elastic blade as the developing sleeve rotates, and the toner is transported to the developing unit facing the photosensitive drum 70. The toner on the developing sleeve is jumped to the electrostatic latent image on the photosensitive drum 70 (70Y to 70K) by the developing voltage obtained by superimposing the AC component on the DC component applied to the developing sleeve, and is attached to the exposed portion of the latent image. The latent image is reversely developed.
[0033]
  The primary transfer roller 54 (54Y to 54K) is formed by coating an EPDM conductive rubber layer over a length of 310 mm on a core metal having a diameter of 8 mm so as to have a diameter of 16 mm. It is connected to a primary transfer power supply 48 (48Y to 48K). The roller hardness of the primary transfer roller 54 is 35 ° in Asker C, and the resistance value of the primary transfer roller abuts on a 30 mm diameter aluminum cylinder rotated at a peripheral speed of 24 mm / sec. Measured under the condition that 50 V is applied between the cylinder and the primary transfer roller, 1 × 10⁶Ω.
[0034]
  The secondary transfer roller 55 is formed by covering a core metal having a diameter of 8 mm with a urethane conductive rubber layer in a longitudinal direction of 310 mm and forming a diameter of 17 mm. The roller hardness is 30 ° in Asker C, and the primary transfer roller The resistance value measured by the same method is 1 × 10⁷Ω. The secondary transfer roller 55 is also connected to a high-voltage power source 49 through a power supply spring. The drive roller 51, the tension roller 52, and the secondary transfer counter roller 53 are all made of an aluminum conductive roller having a diameter of 32 mm, and the cored bar portion is grounded via a power supply spring.
[0035]
  The intermediate transfer belt 80 is a single-layer seamless endless belt made of polyimide resin whose resistance is adjusted by carbon dispersion, and has a thickness of 75 μm, a circumferential length of 1115 mm, and a widthwise length of 310 mm perpendicular to the circumferential direction. . In accordance with JIS-K6911, in order to obtain good contact between the electrode and the surface of the belt, a conductive rubber is used as an electrode, and then the volume resistance of the intermediate transfer belt is measured using an R8340 ultrahigh resistance meter manufactured by Advantest. When the rate ρv and the surface resistivity ρs are measured, ρv = 5 × 10 when 100 V is applied for 10 seconds.⁸Ωcm, ρs> 1 × 10¹³A value of Ω / □ was obtained. It should be noted that ρs has the same result regardless of whether it is measured on the front or back side of the belt.
[0036]
  The tension of the intermediate transfer belt 80 stretched around the three rollers 51, 52 and 53 is 6 kgf. The distance between the drive roller 51 and the tension roller 52 is 500 mm, and is constituted by the photosensitive drum 70 (70Y to 70K) and the primary transfer roller 54 (54Y to 54K) of each image forming station 10 (10Y to 10K). The primary transfer portions are arranged at equal intervals on the intermediate transfer belt 80 between the rollers 51 and 52. Each primary transfer roller 54 is lifted by a spring having a load of 500 gf provided at both ends, and is brought into contact with the back surface of the intermediate transfer belt 80 by a force obtained by pulling the weight 150 g of the primary transfer roller itself.
[0037]
  In this image forming apparatus, the maximum size of the transfer material that can be used is A3. The process speed is 117 mm / second. By setting the primary transfer voltages Vy to Vk to 200 V and the secondary transfer voltage to 2.3 kV, good transferability on plain paper can be obtained for all colors.
[0038]
  Next, the developing device adjustment mode in the image forming apparatus will be described. The developing device adjustment mode in this embodiment is controlled to be executed every time an image is formed on a predetermined number (200 sheets) of transfer material P after the power is turned on and the environment is changed. In addition, when this mode is executed once, the toner images discharged from the developing devices 14 (14Y to 14K) for each color are solid images corresponding to A3 size (main scanning direction 297 mm × sub-scanning direction 410 mm) for each color. The By discharging the toner, various image defects caused by the developing device 14 can be prevented.
[0039]
  When the developing device adjustment mode is started, a yellow solid image is first developed on the photosensitive drum 70Y as an adjustment toner image in the image forming station 10Y. The toner image for adjustment is transferred onto the intermediate transfer belt 80 by applying the same primary transfer voltage Vy = 200 V as that in the normal printing operation by the power supply 48Y in the primary transfer portion of the image forming station 10Y.
[0040]
  The yellow solid image transferred onto the intermediate transfer belt 80 passes through the primary transfer portions of the image forming station 10M, the image forming station 10C, and the image forming station 10K, and then is conveyed to the belt cleaner 33 and collected. Is done. At this time, the primary transfer voltage applied by the power supplies 48M to 48K in the primary transfer units of the image forming station 10M, the image forming station 10C, and the image forming station 10K is Vm, which is a retransfer prevention voltage lower than that in the normal printing operation. = Vc = Vk = 0V. As is clear from FIG. 2, in this image forming apparatus, the retransfer rate is sufficiently low at a voltage of 0 V, and the discharged yellow solid image is retransferred onto the magenta, cyan, and black photosensitive drums 70M to 70K. It is prevented.
[0041]
  Next, in the primary transfer portion of the image forming station 10M immediately after the yellow solid image has passed, the primary transfer voltage is switched from the retransfer prevention voltage Vm = 0V to the normal printing operation voltage Vm = 200V. . Then, the magenta solid image formed so as to reach the primary transfer portion in accordance with the timing when the yellow solid image completes passing on the photosensitive drum 70M is subsequently transferred onto the intermediate transfer belt 80. In addition, by controlling the timing so that the yellow and magenta solid images do not overlap each other on the intermediate transfer belt 80, a transfer efficiency is avoided by transferring the magenta solid image onto the intermediate transfer belt 80, so that the photoconductor Not only the retransfer toner of the yellow solid image but also the transfer residual toner of the magenta solid image can be prevented from staying on the drum 70M.
[0042]
  Following the above, toner discharge at the image forming station 10C and the image forming station 10K is performed in the same manner. During execution of the developing device adjustment mode, the secondary transfer roller 55 is separated from the intermediate transfer belt 80 in order to avoid contamination due to the adjustment toner image on the intermediate transfer belt 80 conveyed to the belt cleaner 33. .
[0043]
  As explained above, the bookReference exampleAccordingly, in the developing device adjustment mode, the transfer voltage at the primary transfer portion of the downstream image forming station and the toner image for adjustment on the photosensitive drum 70 of the downstream image forming station are transferred onto the intermediate transfer belt 80. Control is performed such that the adjustment toner image from the upstream image forming station is smaller when it passes through the downstream image forming station.The transfer voltage is such that the adjustment toner image from the upstream image forming station passes through the downstream image forming station than when the adjustment toner image on the photosensitive drum 70 of the downstream image forming station is transferred onto the intermediate transfer belt 80. It is controlled so that the absolute value is smaller and the voltage has the same polarity when passing.Thus, the adjustment toner image transferred onto the intermediate transfer belt 80 is conveyed to the belt cleaner 33 without being retransferred when passing through the downstream image forming station, and new image defects in subsequent printing are prevented. Can do.
[0044]
  The above mentionedReference exampleIn the image forming apparatus, the resistance value of the primary transfer roller 54 of each image forming station is the same. However, even in an image forming apparatus in which these differ from image forming apparatus station, paying attention to the transfer electric field formed in the primary transfer portion of each image forming station, the transfer electric field of the downstream image forming station is changed to the downstream image forming station. When the adjustment toner image from the upstream image forming station passes through the downstream image forming station is smaller than when the adjustment toner image on the photosensitive drum 70 is transferred onto the intermediate transfer belt 80. The same effect can be obtained by controlling the transfer voltage in this way. This is because a physical phenomenon such as toner transfer or retransfer is essentially caused by the action of a transfer electric field in the nip of the primary transfer portion. Therefore, for example, it is possible to control the transfer electric field in the primary transfer portion by switching the charging voltage applied to the primary charging roller.
[0045]
  Also bookReference exampleIs provided with an auxiliary charger or the like as a toner charging means instead of the drum cleaner 16, and together with the action of the primary charging roller, the developing device as the developing means is again developed after correcting the tribo of residual toner on the photosensitive drum to an appropriate value. The present invention is also applicable to an image forming apparatus that employs a so-called drum cleanerless system that is collected and reused. In such an image forming apparatus, it is more difficult to collect toner staying on the surface of the photosensitive drum than in an image forming apparatus having a drum cleaner, and surface contamination of the photosensitive drum and the primary charging roller also occurs. Since it is easy, it can be said that the present invention is more effective.
[0046]
  (Example 1)
  This exampleReference example 1This is another example related to the developer adjustment mode described in the above.Reference example 1This is the same as in FIG.
[0047]
  Reference example 1In the developing device adjustment mode described above, the amount of toner of each color discharged from the developing device 14 can be set to be increased or decreased as needed according to the total number of prints using the developing device 14 or the environment. In order to discharge an excessive amount of toner from the inside of the developing unit 14 and not increase the toner consumption unnecessarily, it is necessary and sufficient to prevent image defects caused by the developing unit 14 according to the use state of the image forming apparatus. It is necessary to set the mode to discharge the amount of toner.
[0048]
  In this embodiment, the amount of toner of each color discharged when executing a single developer adjustment mode isReference example 1In the case where the number is set to be less than the above, details of implementation of a mode capable of preventing a new image defect after execution of the developing device adjustment mode and suppressing a decrease in throughput in the image forming apparatus will be described.
[0049]
  FIG. 3 is a schematic view of the intermediate transfer belt 80 developed in the circumferential direction (sub-scanning direction). In FIG. 3, Y1 is a yellow solid adjustment toner image developed (discharged) on the photosensitive drum 70Y by the developing unit 14Y in the image forming station 10Y and transferred onto the intermediate transfer belt 80. This toner image has a width (297 mm) corresponding to the A3 size in the main scanning direction. Similarly, M1 is a magenta solid image, C1 is a cyan solid image, and K1 is a black solid adjustment toner image. These adjustment toner images for development adjustment are formed so as not to overlap each other, and an arrow b in the figure indicates the moving direction of the intermediate transfer belt 80.
[0050]
  Further, in the moving direction of the intermediate transfer belt 80, the length of Y1 in the sub-scanning direction is set to be shorter than the distance between the primary transfer portions of the image forming stations 10Y and 10M. Similarly, the length of M1 in the sub-scanning direction, the length of C1 in the sub-scanning direction, and the length of K1 in the sub-scanning direction are similarly the distance between adjacent primary transfer portions (the distance between adjacent primary transfer portions in the image forming apparatus is It is set to be shorter than the same (set to 100 mm).
[0051]
  In this embodiment, since the distance from the leading edge to the trailing edge of each color solid image and the distance between the primary transfer portions are set as described above, the solid images of each color formed on the photosensitive drums 70Y to 70K are displayed. The transfer onto the intermediate transfer belt 80 can be performed almost at the same time. That is, when the transfer of the solid image (for example, Y1) from the photosensitive drum 70 (for example, the photosensitive drum 70Y) to the intermediate transfer belt 80 is completed, the leading edge of the solid image (for example, Y1) on the intermediate transfer belt 80 is completed. ) Does not reach the downstream primary transfer portion (for example, the primary transfer portion of the image forming station 10M).
[0052]
  In this embodiment, for example, after the transfer of the magenta solid image (M1) from the photosensitive drum 70M to the intermediate transfer belt 80 is completed, the intermediate transfer belt 80 formed on the upstream image forming station 10Y is transferred. The voltage applied to the primary transfer roller 54M from the power source 48M before the yellow solid image (Y1) reaches the primary transfer portion of the image forming station 10M is applied voltage Vm at the time of transferring the magenta solid image (M1). The applied voltage Vm for preventing retransfer is switched from 200V to 200V.
[0053]
  Although the above description is for the image forming station 10Y and the downstream image forming station 10M, the image forming station 10M and the downstream image forming station 10C, and the downstream image forming station 10C and the downstream image forming station. The same applies to the case of 10K. Accordingly, in this case, the voltage applied from the power supply 48 to the primary transfer roller 54 in each station 10 is almost simultaneously (timing) from the applied voltage 200 V at the time of transferring each color solid image to the applied voltage 0 V for preventing retransfer. Since switching is performed, switching control is facilitated. Then, the time required for the developing device adjustment mode (the time from the start to the end of the developing device adjustment mode) can be shortened as much as possible.
[0054]
  Therefore, when the developing device adjustment control mode is interrupted halfway before the image formation for a plurality of transfer materials P is completed, the normal image on the next transfer material P is displayed after the developing device adjustment mode is started. Since the time until the start of formation can be shortened, it is possible to prevent a decrease in image formation throughput.
[0055]
  As described above, according to the present exemplary embodiment, in the developer adjustment mode, the length of the adjustment toner image for each color is made shorter than the distance between the adjacent primary transfer portions, the timing is synchronized, and the intermediate The image is transferred onto the transfer belt 80. Further, the transfer voltage at the primary transfer portion of the downstream image forming station is set higher than when the adjustment toner image on the photosensitive drum 70 of the downstream image forming station is transferred onto the intermediate transfer belt 80. The adjustment toner image is controlled so as to be smaller when it passes through the downstream image forming station. As a result, the adjustment toner image transferred onto the intermediate transfer belt is conveyed to the belt cleaner 33 without being retransferred when passing through the downstream image forming station, and a new image defect in subsequent printing is prevented. A decrease in throughput of the image forming apparatus due to mode execution can also be suppressed.
[0056]
  (Reference example 2)
  Figure 4Reference example 22 is a schematic configuration diagram of the image forming apparatus of FIG. BookReference exampleThe image forming apparatus shown in FIG.Reference example 1The intermediate transfer type image forming apparatus is modified from the multiple transfer type image forming apparatus.
[0057]
  BookReference example1 uses a transfer belt 90 which is a belt-shaped transfer material conveyance body instead of the intermediate transfer belt 80 of the image forming apparatus of FIG. 1, and transfers the transfer material P supplied from the feeding roller 20 onto the transfer belt 90. The toner images of the respective colors on the photosensitive drum 70 are transferred onto the transfer material P by a power source (transferred to the photosensitive drum 70 (70Y to 70K) of each of the image forming stations 10Y to 10K. 48Y to 48K), and multiple transfer is performed by the transfer roller 54 (54Y to 54K) to which a transfer voltage is applied. Thereafter, the transfer material P is separated from the transfer belt 90 and conveyed to the fixing device 40, and four color toner images are pressurized and heated to form a full color fixed image. The transfer belt 90 is the same as the intermediate transfer belt 80. By setting the transfer voltages Vy to Vk to 1.5 kV, good transfer properties on plain paper can be obtained for all colors.
[0058]
  For the developer adjustment mode of the image forming apparatus employing such a transfer belt 90,Reference example 1as well asExample 1the same asInCan be applied. That is, in the developing device adjustment mode, the transfer voltage when transferring the adjustment toner image on the photosensitive drum 70 onto the transfer belt 90 is 200 V, and the adjustment toner image passes through the transfer portion of the downstream station. By controlling the transfer voltage to be 0 V, the adjustment toner image transferred onto the transfer belt 90 is conveyed to the belt cleaner 33 without being retransferred when passing through the downstream image forming station, and in subsequent printing New image defects can be prevented.
[0059]
【The invention's effect】
  As described above, in the present invention, when the adjustment toner image formed by another transfer unit passes through the transfer position, a weaker electric field is formed than when each transfer unit forms the adjustment toner image. Therefore, it is possible to prevent a new image defect from occurring after the toner is discharged from the image carrier.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an image forming apparatus.
FIG. 2 is a diagram illustrating a relationship between a transfer voltage, transfer efficiency, and retransfer rate.
[Fig. 3]Example 12 is a diagram in which the intermediate transfer belt is developed in the circumferential direction.
[Fig. 4]Reference example 2It is explanatory drawing of the image forming apparatus of FIG.
[Explanation of symbols]
  P: Transfer material,
  10: Image forming station, 12: Primary charging roller,
  13 ... Laser exposure device, 14 ... Developer, 16 ... Drum cleaner,
  20 ... Feed roller, 33 ... Belt cleaner, 40 ... Fixing device,
  48 ... primary transfer power supply, 49 ... secondary transfer power supply, 51 ... drive roller,
  53 ... Secondary transfer counter roller, 54 ... Primary transfer roller,
  55 ... secondary transfer roller, 70 ... photosensitive drum,
  80 ... intermediate transfer belt, 90 ... transfer belt,

Claims (3)

A plurality of photoreceptors each rotating in the sub-scanning direction;
Exposure means for scanning the photoconductor in a main scanning direction to form an electrostatic latent image;
A plurality of developing units that contain toner and supply toner to each photoconductor to form a toner image;
An intermediate transfer member that rotates in the sub-scanning direction ;
Cleaning means for removing toner adhering to the intermediate transfer member;
Wherein disposed opposite on each photoreceptor, anda plurality of transfer means for transferring the toner image on the intermediate transfer member,
The plurality of photosensitive members are arranged side by side in the rotation direction of the intermediate transfer member, and an adjustment toner image for discharging deteriorated toner from the plurality of developing devices is transferred onto the intermediate transfer member to adjust image quality. In the image forming apparatus to
Forming an adjustment toner image having a length in the sub-scanning direction shorter than a distance between transfer positions of the adjacent transfer units on each of the photoconductors by the developing units;
The plurality of adjustment toner images formed are transferred onto the intermediate transfer body almost simultaneously by the plurality of transfer means,
At each transfer position of said plurality of transfer means, when adjusting toner image it from being transferred in the upstream side of the transfer means relates the rotational direction of the intermediate transfer member passes through the transfer position, the intermediate said adjusting toner image An image forming apparatus, wherein an electric field weaker than that when transferred to a transfer body is formed. A plurality of photoreceptors each rotating in the sub-scanning direction;
Exposure means for scanning the photoconductor in a main scanning direction to form an electrostatic latent image;
A plurality of developing units that contain toner and supply toner to each photoconductor to form a toner image;
A transfer material carrier that carries the transfer material and rotates in the sub-scanning direction;
Cleaning means for removing toner adhering to the transfer member carrier;
A plurality of transfer means arranged to face each of the photoconductors and transferring a toner image onto the transfer material,
The plurality of photoconductors are arranged side by side in the rotation direction of the transfer material carrier, and an adjustment toner image for discharging deteriorated toner from the plurality of developing devices is transferred onto the transfer material carrier. In the image forming apparatus for adjusting the quality,
Forming an adjustment toner image having a length in the sub-scanning direction shorter than a distance between transfer positions of the adjacent transfer units on each of the photoconductors by the developing units;
The plurality of adjustment toner images formed are transferred onto the transfer material carrier almost simultaneously by the plurality of transfer means,
At each transfer position of the plurality of transfer means, when the adjustment toner image transferred by the transfer means upstream of the transfer material carrier in the rotation direction passes through the transfer position, the adjustment toner image is An image forming apparatus, wherein an electric field weaker than that when transferred to a transfer material carrier is formed . 3. The applied voltage is switched to zero when an adjustment toner image transferred by another transfer unit passes through each transfer position of the plurality of transfer units. Image forming apparatus .

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