JP5381425B2 - Image forming apparatus - Google Patents

Description

  The present invention not only prevents an abnormal white silica band that occurs in a formed image when developing by contact charging or contact development using toner containing externally added fine particles, but also prolongs the life of the photosensitive drum. The present invention relates to a forming apparatus.

  Conventionally, there is an electrophotographic image forming apparatus. In this image forming apparatus, generally, a photosensitive drum is uniformly charged and initialized, an electrostatic latent image is formed on the photosensitive drum by optical writing, and the electrostatic latent image is converted into a toner image. Is directly or indirectly transferred onto a transfer material such as paper and fixed by a fixing device.

  In the past, corona discharge-type chargers and transfer devices were used for the above charging and transfer, but in recent years, contact-type chargers and transfer devices have increased due to the problem of deterioration of the usage environment due to ozone generation. . For example, a contact-type charger is known in which a conductive foam is formed on a core metal and a polyurethane skin layer is formed on the surface of the conductive foam (for example, Patent Document 1). reference).

  Similarly, as a contact-type charger, a charger having a conductive resin tube coated with a conductive foam having a metal core has been proposed as a small-sized and long-life charger (see, for example, Patent Document 2).

  Further, as a developing device, a non-magnetic one-component developing device in which a non-magnetic one-component toner is used as a toner to be used and the inside of the toner hopper is doubled so as to be able to be enlarged is known (for example, (See Patent Document 3).

  By the way, the non-magnetic one-component toner used in the conventional electrophotographic image forming apparatus includes, for example, silica treated with silicon oil, titania, etc. in order to improve toner fluidity and prevent toner aggregation. An external additive composed of fine particles is added to the toner.

  Further, when the image forming apparatus is not operating, the photosensitive drum and the developer carrying roller are in pressure contact with each other along a line along the axial direction of the peripheral surface. When the image forming apparatus is activated and starts operating, the image formed on the first sheet of paper is whitened at the portion where the developer carrying roller and the photosensitive drum are in contact with each other while the image forming apparatus is stopped. In general, a phenomenon called “silica white band” occurs.

  This is because silica or titania or the like externally added to the toner on the developer carrying roller is treated with silicon oil, so that the oil component contacts the developer carrying roller and the photosensitive drum while it is stopped. It has been found that this is because the toner is transferred to the photosensitive drum at that portion, and the toner becomes difficult to be developed at that portion.

  Therefore, in order to prevent the occurrence of this silica white band phenomenon, prior to the development of the toner by the photosensitive drum and the developer carrying roller, the photosensitive drum and the developer carrying roller are After idling to some extent (rotation of play without development processing), the oil component on the photosensitive drum was scraped off by a cleaning blade, etc., then moved to actual image formation processing and contacted during stoppage It has been practiced to prevent the phenomenon of streaking at the part.

Japanese Patent Application Laid-Open No. 07-092774 JP-A-11-125956 JP 2001-194 483 A

  By the way, if the photosensitive drum and the developer carrying roller are idly rotated in order to prevent the silica white band, the photosensitive layer of the photosensitive drum is scraped along with the idling, and the photosensitive drum is exposed regardless of the actual image forming process. There was a problem of significantly shortening the life of the body drum.

  Further, since the photosensitive drum and the developer carrying roller are idled before the actual image forming process is started, the elapsed time until the image-formed paper is discharged, that is, the first image is formed. There is a problem that it takes a long time until the discharged paper is discharged, which is inconvenient for the user.

In order to solve the above problems, an image forming apparatus according to the present invention includes at least a photosensitive drum, a charging unit that charges the photosensitive drum to a predetermined potential, and the photosensitive drum that is charged by the charging unit. An electrostatic latent image forming unit that forms an electrostatic latent image according to an image signal, and a toner having external fine particles added to the electrostatic latent image formed on the photosensitive drum, and according to the image signal An image forming unit having a developer carrying roller that develops the toner image, and a transfer unit that performs image formation on the transfer material by transferring the toner image developed by the developer carrying roller onto the transfer material; At the start-up of the image forming unit, at least before the formation of the electrostatic latent image on the photosensitive drum and before the toner is applied to the photosensitive drum by the developer carrying roller, A rotation drive control unit for rotating the optical drum and the developer carrying roller a predetermined time, assuming an image forming apparatus having a counter for counting the transfer count to the transfer material.

The toner is a non-magnetic one-component toner externally added with silica or titania fine particles treated with silicone oil, and the rotation drive control unit rotates the photosensitive drum or the developer for the predetermined time. Only the period from when the agent-carrying roller is new to when the count value of the number of transferred sheets by the counter reaches a predetermined count value, and when the predetermined count value is exceeded, the rotation is not performed for the predetermined time. It is configured to control to execute image formation by the image forming unit.

The predetermined count value is set so that, for example, the transfer of the toner image is 3000 sheets when the transfer material is A4 size .

  In addition, the period during which the rotation for the predetermined time is performed is, for example, a period until an inconspicuous state in which a white image is missing from the formed image when an image is formed on the transfer material.

  In the present invention, the idle rotation at the start-up start-up is not performed for an unlimited period, but only during the period until the defect due to the external additive of the formed image becomes inconspicuous. In addition to the effect of preventing the band, the surface of the photosensitive drum is not scraped over a long period of time regardless of the actual image forming process, and the lifetime of the photosensitive drum is prolonged.

1 is a cross-sectional view illustrating an internal configuration of a full-color image forming apparatus (printer) according to Embodiment 1 of the invention. 1 is a circuit block diagram including a printer control device according to a first embodiment of the present invention. FIG. 1 is a cross-sectional view illustrating an image forming unit of a printer according to Embodiment 1 of the present invention. (a) is a diagram showing the results of detailed examination of the occurrence of silica white bands, and (b) is a diagram showing the development timing of a toner image that prevents the occurrence of silica white bands based on the results of (a). . FIG. 6 is a diagram showing that after printing 3000 sheets of A4 size paper, a silica white band is not recognized even if printing is started immediately at the start of printing after a pause. When the number of printed sheets of the printer according to Embodiment 1 of the present invention or the rotation time of the developing roller exceeds a predetermined amount, preparatory rotation at the start of printing of the photosensitive drum is prohibited and printing is started from the rotation immediately after the start of printing. It is a flowchart which shows control of a process.

  Hereinafter, embodiments of the present invention will be described in detail. In the following description, the charging means described in the means for solving the above-described problems is composed of, for example, the charging roller 9 and the electrostatic latent image forming means is composed of, for example, the optical writing head 11 and the like. The roller is composed of, for example, the developing roller 13, and the transfer means is composed of, for example, the photosensitive drum 7, the transfer belt 14, the primary transfer roller 18, the secondary transfer roller 26, and the rotation drive control unit is, for example, PR-CONT 37, a printer printing unit. 38 mag.

  In the following description, the image forming unit described in the means for solving the problems includes the image forming unit 2, the intermediate transfer belt unit 3, the paper feeding unit 4, the duplex printing transport unit 5, and the CPU 35 shown in FIG. And other control devices.

  FIG. 1 is a cross-sectional view illustrating an internal configuration of a full-color image forming apparatus (hereinafter simply referred to as a printer) according to Embodiment 1 of the present invention. A printer 1 shown in FIG. 1 is an electrophotographic secondary transfer tandem color image forming apparatus, and includes an image forming unit 2, an intermediate transfer belt unit 3, a paper feeding unit 4, and a duplex printing conveyance unit 5. It consists of

  The image forming unit 2 has a configuration in which four image forming units 6 (6M, 6C, 6Y, and 6K) are arranged in a multistage manner from right to left in FIG.

  Of the four image forming units 6, three image forming units 6M, 6C and 6Y on the upstream side (the right side in the figure) are magenta (M), cyan (C) and yellow (subtractive three primary colors, respectively). A mono-color image is formed with the color toner of Y), and the image forming unit 6K forms a monochrome image with black (K) toner mainly used for dark portions of characters and images.

  Each of the image forming units 6 has the same configuration except for the color of the toner stored in the toner container (toner cartridge). Accordingly, the configuration of the black (K) image forming unit 6K will be described below as an example.

  The image forming unit 6 includes a photosensitive drum 7 at the bottom. The peripheral surface of the photosensitive drum 7 is made of, for example, an organic photoconductive material. A cleaner 8, a charging roller 9, an optical writing head 11, and a developing roller 13 of the developing device 12 are arranged around the periphery of the photosensitive drum 7.

  The developing device 12 is provided in the upper toner container as shown by M, C, Y, and K in the drawing, and is one of magenta (M), cyan (C), yellow (Y), and black (K) developers. (Toner) is accommodated, and a toner replenishing mechanism for the lower part is provided in the intermediate part.

  These toners are non-magnetic one-component toners to which an external additive composed of fine particles such as silica or titania treated with silicon oil is added. If the toner external additive is treated with silicon oil, filming of the photosensitive drum can be prevented and the life of the photosensitive drum can be extended.

  Further, the developing roller 13 is provided in the lower side of the developing device 12 in the side opening, and a toner stirring member, a toner supply roller for supplying toner to the developing roller 13, and a toner layer on the developing roller 13 are fixed. It has a doctor blade that regulates the layer thickness.

  The intermediate transfer belt unit 3 has an endless transfer belt 14 extending in a flat loop shape from substantially the left and right sides of the figure at the approximate center of the main unit, and the transfer belt 14 is stretched over the transfer belt 14. A belt driving roller 15 and a driven roller 16 are provided to circulate and move the belt 14 counterclockwise in the figure.

  The transfer belt 14 transfers the toner image directly to the belt surface (primary transfer), and further transfers the toner image to a recording medium (hereinafter also referred to as paper) (secondary transfer). Here, the entire unit is referred to as an intermediate transfer belt unit.

  The intermediate transfer belt unit 3 includes a belt position control mechanism 17 in the loop of the flat loop-shaped transfer belt 14. The belt position control mechanism 17 includes a primary transfer roller 18 made of a conductive foam sponge that presses against the lower peripheral surface of the photosensitive drum 7 via the transfer belt 14.

  The belt position control mechanism 17 has three primary transfer rollers 18 corresponding to the three image forming units 6M, 6C, and 6Y of magenta (M), cyan (C), and yellow (Y) as vertical support shafts. Rotate to the center with the same period.

  Then, the belt position control mechanism 17 rotates and moves one primary transfer roller 18 corresponding to the black (K) image forming unit 6K at a rotational movement cycle different from the cycle of the three primary transfer rollers 18. The belt 14 is moved away from the photosensitive drum 7.

  That is, the belt position control mechanism 17 moves the position of the transfer belt 14 of the intermediate transfer belt unit 3 to full color mode (all four primary transfer rollers 18 are in contact with the transfer belt 14), monochrome mode (to the image forming unit 6K). Only the corresponding primary transfer roller 18 is in contact with the transfer belt 14) and all non-transfer modes (all four primary transfer rollers 18 are separated from the transfer belt 14).

  In the intermediate transfer belt unit 3, a belt cleaning unit 34 is disposed further upstream of the uppermost image forming unit 6 </ b> M in the belt moving direction on the upper surface, and the belt lower surface is substantially along the entire surface. A flat and thin waste toner collecting container 19 is detachably disposed.

  The paper feed unit 4 includes two paper feed cassettes 21 arranged in two upper and lower stages, and in the vicinity of the paper feed opening (right side in the figure) of the two paper feed cassettes 21, respectively, A feeding roller 23, a separating roller 24, and a standby conveying roller pair 25 are disposed.

  In the paper conveyance direction (vertical upward direction in the figure) of the standby conveyance roller pair 25, a secondary transfer roller 26 that is in pressure contact with the driven roller 16 via the transfer belt 14 is disposed, and the secondary transfer portion to the paper is arranged. Forming.

  A belt-type fixing device 27 is disposed on the downstream side (upward in the drawing) of the secondary transfer unit, and the fixed sheet is carried out of the belt-type fixing device 27 further downstream of the belt-type fixing device 27. A pair of carry-out rollers 28 and a pair of paper discharge rollers 31 that discharge the discharged paper to a paper discharge tray 29 formed on the upper surface of the apparatus are disposed.

  The duplex printing conveyance unit 5 includes a start return path 32a that branches from the intermediate conveyance path between the carry-out roller pair 28 and the discharge roller pair 31 to the right lateral direction in the drawing, and then an intermediate return path 32b that bends downward. A terminal return path 32c that bends in the left lateral direction opposite to the above and eventually reverses the return sheet, and four return roller pairs 33a, 33b, 33c, and 33d disposed in the middle of these return paths. ing.

  The exit of the end return path 32 c communicates with a conveyance path to the pair of standby conveyance rollers 25 corresponding to the sheet feeding cassette 21 below the sheet feeding unit 4. In this example, the belt cleaning unit 34 described above is disposed on the upper surface of the intermediate transfer belt unit 3.

  The belt cleaning unit 34 comes into contact with the upper surface of the transfer belt 14 to scrape and remove the waste toner, and stores it in a temporary storage unit of a belt cleaner unit (not shown). The stored waste toner is dropped by a conveying screw. The inside of the cylinder is conveyed to the upper part, and is sent to the waste toner collecting container 19 through the dropping cylinder.

  As shown in FIG. 1, the printer 1 is not a system that directly transfers a toner image onto a sheet, but a sheet conveyed in the vertical direction to a secondary transfer unit by a standby conveyance roller pair 25 via an intermediate transfer belt 14. The toner image is transferred.

  Therefore, it is possible to cope with a maintenance process for recovering from a problem such as a paper jam occurring in the paper transport path by simply opening the right side of FIG.

  In addition, since troubles such as paper jam do not occur in the arrangement section of the kits, the operation for attaching and detaching consumables such as the kits concentrated on the left side of FIG. 1 may be a small space that can be replaced in the longitudinal direction. It is configured as follows.

  Thereby, the dimension between kits is reduced as much as possible, and size reduction of the whole apparatus main body is achieved. Further, the optical writing head itself is also miniaturized and is configured closer to the photosensitive drum.

  FIG. 2 is a circuit block diagram including the control device of the printer 1 described above. As shown in FIG. 2, the circuit block has a CPU (central processing unit) 35 as a center, and an interface controller (I / F_CONT) 36 and a printer controller (PR_CONT) 37 are connected to the CPU 35 via data buses. ing. A printer printing unit 38 is connected to the PR_CONT 37.

  Connected to the CPU 35 are a read only memory (ROM) 39, an electrically erasable programmable ROM (EEPROM) 41, an operation panel 42 of the main body operation unit, and a sensor unit 43 to which outputs from sensors arranged in the respective units are input. Has been. A system program is stored in the ROM 39, and the CPU 35 performs processing by controlling each unit in accordance with the system program.

  That is, in each unit, first, the I / F_CONT 36 converts print data supplied from a host device such as a personal computer into bitmap data and develops it in the frame memory 44. In the frame memory 44, a storage area is set for each of black (K), magenta (M), cyan (C), and yellow (Y), and data of each color is developed in a corresponding area.

  The data expanded in the frame memory 44 is output to the PR_CONT 37, and is output from the PR_CONT 37 to the printer printing unit 38.

  The printer printing unit 38 is an engine unit, and under the control of the PR_CONT 37, the rotation driving system including the photosensitive drum 7, the primary transfer roller 18 and the like shown in FIG. 1, the charging roller 9, the optical writing head 11, etc. A drive output to a process load such as an applied voltage of an image forming unit having a driven portion is controlled.

  Further, the printer printing unit 38 includes a belt driving unit 45 that performs the vertical movement of the intermediate transfer belt unit 3, the rotation driving of the transfer belt 14, the belt driving of the belt-type fixing device 27, the sheet take-out roller 22 to the discharge roller pair 31, and the like. The drive output to the transport mechanism drive unit 46 that drives the transport mechanism composed of the various parts that are rotationally driven is controlled.

  The black (K), magenta (M), cyan (C), and yellow (Y) data output from the PR_CONT 37 are respectively sent from the printer printing unit 38 to the corresponding optical writing head 21 shown in FIG. To be supplied.

  FIG. 3 is a cross-sectional view showing the image forming unit 6. In FIG. 3, the same components as those in FIG. 1 are denoted by the same reference numerals as those in FIG. Further, the optical writing head 11 and the transfer belt 14 which are engaged when the image forming unit 6 is mounted on the main body apparatus are indicated by two-dot chain phantom lines.

  As shown in FIG. 3, the image forming unit 6 includes a developing unit 12 including a toner cartridge 47 and a developing unit 49 including an exterior frame 48, and a drum unit that is assembled with the exterior frame 48 and integrated with the developing unit 12. And 50.

  The drum unit 50 incorporates the photosensitive drum 7, the cleaner 8, the charging roller 9 and the like shown in FIG. 1, and the developing unit 49 of the developing device 12 includes the supply roller 19 and the developing roller 13 shown in FIG. 1. In addition, a doctor blade 51, a stirrer 52, and the like are disposed.

  One drum unit 50 is cleaned by the cleaning blade of the cleaner 8 and uniformly initialized by the charging roller 9 on the peripheral surface of the photosensitive drum 7. Accordingly, exposure is performed, and an electrostatic latent image is formed which includes a high voltage portion of initial charging and a low voltage portion attenuated by exposure.

  The electrostatic latent image moves to a developing position a formed by the facing portion of the photosensitive drum 7 and the developing roller 13 as the photosensitive drum 7 rotates counterclockwise as indicated by an arrow. .

  The other developing unit 49 always stores toner supplied from the upper toner cartridge 47. The stirrer 52 stirs the toner so that it does not coagulate, and the supply roller 19 supplies the toner to the peripheral surface of the developing roller 13 while rotating in the same direction as the developing roller 13 as indicated by an arrow.

  The toner supplied to the peripheral surface of the developing roller 13 is regulated to a certain thickness by a doctor blade 51 disposed on the downstream side in the conveying direction (rotating direction) of the developing roller 13, and is rotated and conveyed to the developing position a. Is done.

  The toner rotated and conveyed to the developing position a is transferred to the low potential portion of the electrostatic latent image due to the potential difference between the peripheral surfaces of the developing roller 13 and the photosensitive drum 7, whereby the low potential portion of the electrostatic latent image is transferred to the toner. And the image is developed on the peripheral surface of the photosensitive drum 7.

  The toner image developed on the peripheral surface of the photoconductive drum 7 is rotated and conveyed to a transfer portion where the transfer belt 14 and the photoconductive drum 7 are arranged to face each other, and is transferred from the primary transfer roller 18 shown in FIG. The electrostatic latent image applied to 14 is transferred to the primary transfer belt 14 by charges having a polarity opposite to that of the low potential portion of the electrostatic latent image.

  The cleaner 8 is initialized and charged by scraping the toner remaining on the peripheral surface of the photosensitive drum 7 after the toner image is transferred to the primary transfer belt 14 from the peripheral surface of the photosensitive drum 7 by the cleaning blade. It has the role of uniformly cleaning the peripheral surface of the photosensitive drum 7 before being transferred.

  The toner image transferred to the primary transfer belt 14 is conveyed to a secondary transfer unit in which the driven roller 16 and the secondary transfer roller 26 shown in FIG. The toner image transferred to the transfer material (paper) fed from 21 to the secondary transfer unit and transferred is fixed on the surface of the paper by the belt type fixing device 27, and the paper on which the toner image is fixed is carried out. The paper is discharged onto the paper discharge tray 29 by the roller pair 28 and the paper discharge roller pair 31.

  By the way, when the image forming apparatus 1 is stopped or stopped, the photosensitive drum 7 and the developing roller 13 remain in contact with each other at the developing position a shown in FIG. Further, the developing device 12 of this example is a contact non-magnetic one-component developing type developing device using a non-magnetic one-component toner to which an external additive composed of fine particles such as silica or titania treated with silicon oil is added.

  When the development of the toner image is executed immediately after the image forming apparatus 1 starts operation by such a contact non-magnetic one-component development method, the portion where the photosensitive drum 7 and the developing roller 13 are in contact with each other becomes white and streaks. As described above, a phenomenon called “silica white band” in which an image is lost occurs.

  FIG. 4 (a) is a diagram showing the results of detailed examination of the occurrence of silica white bands, and FIG. 4 (b) is a toner that prevents the generation of silica white bands based on the results of FIG. 4 (a). It is a figure which shows the image development timing.

  4 (a) and 4 (b) both show the number of rotations when the position when the photosensitive drum 7 is stopped is the rotation number 0, and then the toner developed corresponding to the rotation number of the photosensitive drum 7 is shown. An image is shown, and below, an evaluation of the state of occurrence of a silica white band in the toner image is shown.

  Further, as evaluation, “X” indicates that the white silica band is conspicuous, “△” indicates that the image is not so noticeable but impairs the image quality, and “○” indicates that the image is hardly noticeable or not at all noticeable. ".

  In the development of the toner image and the transfer to the paper (hereinafter simply referred to as printing or printing), as described above, the silica white band becomes thinner as the photosensitive drum 7 rotates after the printing starts, It will reach an unrecognizable stage.

  As shown in FIG. 4 (a), when the continuous two-sheet printing is performed, the generation state of the silica white band is the second rotation of the photosensitive drum 7 (the first rotation needs to be cleaned before the initialization charging). A clear white silica band appears from the leading edge to the trailing edge on the first sheet of paper from which printing is not possible.

  However, the silica white band is not visible at the rear end of the second sheet corresponding to printing from the seventh rotation of the photosensitive drum 7. The silica white band slightly seen in the front part is also evaluated as “◯”.

  However, the generation of the silica white band up to the sixth rotation of the photosensitive drum 7 at the start of printing is the next printing when the printing is stopped and the photosensitive drum 7 is stopped in contact with the developing roller 13. Occasionally, as shown in FIG. 4 (a), the first printing starts again from the first sheet.

  Conventionally, in order to prevent the generation of such a silica white band, the first printing at the start of printing is started after the rotation of the photosensitive drum 7 after seven revolutions as shown in FIG. 4 (b). It was mentioned before. However, as described above, the wear of the photoconductive drum 7 progresses early and the life of the photoconductive drum 7 is shortened.

  Therefore, as a result of examining the generation status of silica white band in more detail, as the number of printed sheets increases, the generation method becomes gentler, even if the rotational speed of the photosensitive drum is small at the start of printing after the printing pause, It was found that the silica white band was hardly recognized.

  FIG. 5 shows that after printing 3000 sheets of A4 size paper, even if printing is started immediately at the start of printing after pausing, that is, even if printing is started from the second week of rotation of the photosensitive drum 7, the silica white band It is a figure which shows that is hardly recognized.

  As a result of examining the reason, it was found that as the number of printed sheets progressed, silica, titania, etc. added to the toner were embedded in the toner, and the influence of silicon oil on the toner surface was reduced. It was.

  This is because the printing rate of the pattern to be printed is high, and even if new toner is replenished one after another, toner flows inside the developing tank, and there is a lot of accumulated toner, especially at both ends of the developing roller. It is thought that this is because the external additives of the toner are embedded in the toner while rotating inside the developing tank.

  It is clear that the silica white band is likely to occur at the end of the developing roller in contact non-magnetic one-component development because of its structure, but the influence of the toner external additive at the end is reduced, so the number of printed sheets is large. Thus, that is, it is considered that it is less likely to occur as the rotation time of the developing roller advances.

  Since the present invention was developed based on the generation characteristics of the silica white band as described above, when the number of printed sheets or the rotation time of the developing roller exceeds a predetermined amount, the printing start shown in FIG. Occasionally, the preparation rotation for rotating the photosensitive drum 7 six times is eliminated, thereby suppressing the wear of the photosensitive drum 7 and extending the life of the photosensitive drum 7.

  FIG. 6 shows a process of prohibiting the preparatory rotation at the start of printing of the photosensitive drum when the number of printed sheets or the rotation time of the developing roller exceeds a predetermined amount, and starting printing from the rotation immediately after the start of printing (the first and half rounds). It is a flowchart of the rotational drive control which shows this control. The rotation drive control process is a process performed by a control unit including the PR-CONT 37, the printer printing unit 38, and the like including the CPU 35 shown in FIG.

  Further, the “developing part” appearing in the description of the flowchart is a term including the photosensitive drum 7 and the developing roller 13 that form the developing position a shown in FIG. 3, and “delay” is 4B is a term indicating that printing starts after the rotation of the photosensitive drum 7 shown in FIG. The image forming apparatus 1 of the present example is provided with a detection mechanism (not shown) for detecting whether or not the developing unit is new.

  First, the control unit determines whether or not the developing unit is new by detection by the detection mechanism before starting the printing operation (step S01). In the case of a new product (Y in S01), the rotation counter that measures how much the developing unit (for example, the photosensitive drum 7) has been rotated is reset (step S02), and then the generation of a white silica band is prevented. The printing operation in the sequence with delay is set and the printing operation is performed (step S03).

  Next, it is determined whether or not the designated number of printing operations have been completed (step S04). If the printing is finished (S04 is Y), the printing operation is stopped and finished. On the other hand, if not completed (N in S04), the count value of the rotation counter is referred to and the count value is set to a predetermined value (for example, the photosensitive drum 7 prints 3000 sheets in terms of A4 size paper). It is determined whether or not the rotation has reached (step S05).

  When the count value of the rotation counter does not reach a predetermined value (N in S05), the process returns to step S03, and the processes in steps S03 and S04, or steps S03 to S05 are repeated.

  As a result, when the developing unit is new, the rotation counter is initialized to “0”, and the printing operation by the sequence with delay is continued while the rotation of the photosensitive drum 7 is counted by the rotation counter.

  On the other hand, if it is determined in step S01 that the developing unit is not new (S01 is N), since the rotation count of the photosensitive drum 7 by the rotation counter has already been accumulated in the previous printing process, the step is immediately performed. The process proceeds to S05.

  Also in this case, when the count value of the rotation counter does not reach the predetermined value determined in step S05 (N in S05), the process returns to step S03, and steps S03 and S04, or steps S03 to S03- The process of S05 is repeated.

  Eventually, if it is determined in step S05 that the count value of the rotation counter has reached a predetermined value (3000 sheets of A4 size paper have been printed) (S05 is Y), printing is performed. Even if printing is performed immediately after the start, the development unit is in a state where no silica white band is generated. An operation is performed (step S06).

  Next, it is determined whether or not the designated number of printing operations have been completed (step S07). If completed (Y in S07), the printing operation is stopped and the process is terminated.

  On the other hand, when the printing operation for the designated number of sheets has not been completed (N in S07), it is subsequently determined whether or not the developing unit has reached the end of its life (step S08). In this process, for example, it is determined whether or not 30000 sheets have been printed in terms of A4 size paper. Usually, the photosensitive drum or the developing roller reaches the end of life after printing 20000 to 30000 sheets. In this example, it is assumed that a developing unit that reaches the end of its life after printing 30000 sheets is used.

  If it is determined in step S08 that the developing unit has not reached the end of its life (S08 is N), the process returns to step S06, and steps S06 and S07, or steps S06 to S08 are repeated.

  On the other hand, if it is determined in step S08 that the developing unit has reached the end of life (S08 is Y), then, for example, a life notification display such as “Replace the developing unit has reached its end of life” is displayed. The information is displayed on the display unit of the operation panel (step S09), the printing operation is stopped, and the process is terminated.

  As described above, according to the present invention, when the total number of printing processes since the developing unit is new is, for example, 3000 sheets or more (rotation counter exceeds a predetermined value), the generation of a silica white band is prevented. The printing operation is performed by a sequence without delay without preparation rotation.

  Until the cumulative value of the rotation counter exceeds the predetermined value and it is detected that the developing unit has reached the end of its life, the printing operation in the sequence without delay is continued. Is minimized, and as a result, the life of the photosensitive drum can be extended.

  The number of revolutions of the photosensitive drum varies depending on the amount of silicon oil-treated external additive that is externally added to the toner, and the predetermined value of the rotation counter depends on the structure of the developing unit and the supply port for supplying toner. Of course, it depends on the size.

  As a specific example of the present invention, a contact type using a toner having a volume average particle diameter of 8 μm and a toner obtained by externally adding 0.75% of titania treated with silicon oil as well as 2.9% of silica treated with silicon oil. As a result of a test using a non-magnetic one-component developing device, no silica white band was seen after continuous printing corresponding to 3000 sheets of A4 size paper. In this case, the predetermined time is A4. This means the time for printing the equivalent of 3000 sheets.

  As described above, according to the present invention, the idle rotation (preparation rotation) at the start-up start-up is not performed for an unlimited period, but only during a period until the defect due to the external additive becomes inconspicuous. Printing is performed without idling (preparation rotation) until it reaches, so that not only the white band generated at the contact portion between the photosensitive drum and the developing roller is prevented, but also the photosensitive drum can be used regardless of the actual image forming process. Since the surface is not shaved for a long time, the life of the photosensitive drum is prolonged.

  In addition, after a period until the defect due to the external additive becomes inconspicuous, printing is performed without idling (preparation rotation) until the developing unit reaches the end of its life, so the printing start time at start-up after printing suspension Shorter and more productive.

  INDUSTRIAL APPLICABILITY The present invention can be used to prevent abnormalities occurring in a formed image of an image forming apparatus that performs development by contact charging or contact development using toner containing externally added fine particles.

1 Image forming device (printer)
2 Image forming unit 2,
DESCRIPTION OF SYMBOLS 3 Intermediate transfer belt unit 4 Paper feeding part 5 Duplex printing conveyance unit 6 (6M, 6C, 6Y, 6K) Image forming unit 7 (7m, 7c, 7y, 7k) Photosensitive drum 8 Cleaner 9 Charging roller 11 Optical writing Head 12 Developing device 13 Developing roller 14 Transfer belt 15 Drive roller 16 Driven roller 17 Belt position control mechanism 18 Primary transfer roller 19 Supply roller 20 Waste toner recovery container 21 Paper feed cassette 22 Paper take-out roller 23 Feed roller 24 Rolling roller 25 Standby Conveying roller pair 26 Secondary transfer roller 27 Belt type fixing device 28 Unloading roller pair 29 Paper discharge tray 31 Paper discharge roller pair 32a Start return path 32b Intermediate return path 32c End return path 33a, 33b, 33c, 33d Return roller pair 34 Belt Cleaning section 35 CPU (central processing u nit)
36 Interface Controller (I / F_CONT)
37 Printer Controller (PR_CONT)
38 Printer printing section 39 ROM (read only memory)
41 EEPROM (electrically erasable programmable ROM)
42 Operation Panel 43 Sensor Unit 44 Frame Memory 45 Belt Drive Unit 46 Conveying Mechanism Drive Unit 47 Toner Cartridge 48 Exterior Frame 49 Development Unit 50 Drum Unit 51 Doctor Blade 52 Stirrer

Claims (3)

At least a photosensitive drum, charging means for charging the photosensitive drum to a predetermined potential, and electrostatic latent image formation for forming an electrostatic latent image corresponding to an image signal on the photosensitive drum charged by the charging means Means, a developer carrying roller that applies toner having external fine particles to the electrostatic latent image formed on the photosensitive drum and develops a toner image according to the image signal, and the developer carrying roller. An image forming unit having transfer means for executing image formation on the transfer material by transferring the developed toner image onto the transfer material, and at the start-up of the image forming unit, Before forming the electrostatic latent image and before applying the toner to the photosensitive drum by the developer carrying roller, at least the photosensitive drum and the developer carrying roller are rotated for a predetermined time. It has a rotation drive control unit, a counter for counting the transfer count to the transfer material, and
The toner is a non-magnetic one-component toner externally added with silica or titania fine particles treated with silicon oil,
The rotation drive control unit rotates the predetermined time only during a period from when the photosensitive drum or the developer carrying roller is new to when the count value of the number of transferred sheets by the counter reaches a predetermined count value, An image forming apparatus, wherein when the predetermined count value is exceeded, control is performed to execute image formation by the image forming unit without performing rotation for the predetermined time.   2. The image forming apparatus according to claim 1, wherein the predetermined count value is 3000 in terms of the number of transferred toner images when the size of the transfer material is A4 size. The period during which the rotation for the predetermined time is performed is a period until an inconspicuous state in which an image is formed in white and streaks in a formed image when image formation is performed on the transfer material becomes inconspicuous. The image forming apparatus according to 1 or 2 .