Image forming apparatus

Abstract

To provide an image forming apparatus that can prevent the occurrence of dirt on the back of paper and the occurrence of faulty cleaning.SOLUTION: An image forming apparatus comprises: an image carrier; a transfer member that is in contact with the image carrier to form a transfer nip; bias application means that applies, to the transfer nip, a transfer bias for transferring a toner image on the image carrier to a recording medium; and a cleaning member that cleans a surface of the image carrier. The image forming apparatus has a cleaning operation of applying, to the transfer nip, at least a plus bias such as a reverse polarity bias having a polarity opposite to the polarity of the transfer bias to move an attachment attached to the transfer member to the image carrier, thereby cleaning the transfer member. The image forming apparatus forms a plurality of scraping patterns Kp such as toner image patterns not to be transferred to the recording medium at a predetermined interval, and causes the plurality of toner image patterns to pass through the transfer nip during the application of the reverse polarity bias in the cleaning operation.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] Conventionally, there has been known an image forming apparatus that includes an image carrier, a transfer member that contacts the image carrier to form a transfer nip, a bias application means that applies a transfer bias to the transfer nip to transfer a toner image on the image carrier to a recording medium, and a cleaning member that cleans the surface of the image carrier.

[0003] Patent document 1 describes an image forming device in which a toner image pattern is formed to remove filming on an intermediate transfer belt, which serves as an image carrier, and this toner image pattern is passed through a transfer nip and input to the contact point of the cleaning member with the image carrier by the movement of the intermediate transfer belt. Summary of the Invention [Problem to be solved by the invention]

[0004] However, there is a risk of back staining, in which the back surface of the recording medium is soiled, and of poor cleaning. [Means for solving the problem]

[0005] In order to solve the above-mentioned problems, the present invention provides an image forming apparatus comprising an image carrier, a transfer member that contacts the image carrier to form a transfer nip, a bias application means that applies a transfer bias to the transfer nip for transferring a toner image on the image carrier to a recording medium, and a cleaning member that cleans the surface of the image carrier, the image forming apparatus having a cleaning operation that applies at least a reverse polarity bias that is opposite in polarity to the transfer bias to the transfer nip, moves adhesions attached to the transfer member to the image carrier, and cleans the transfer member, forms a plurality of toner image patterns that are not transferred to the recording medium at a predetermined interval, the length of the toner image patterns in the surface movement direction of the image carrier is shorter than the circumferential length of the transfer member, the interval between the toner image patterns is greater than the circumferential length of the transfer member, and the plurality of toner image patterns are passed through the transfer nip when the reverse polarity bias is applied in the cleaning operation. Effect of the Invention

[0006] According to the present invention, the occurrence of back stains and cleaning defects can be suppressed. [Brief description of the drawings]

[0007] [Figure 1] 1 is a schematic diagram of a tandem type color copier (hereinafter simply referred to as a copier) which is an image forming apparatus according to an embodiment of the present invention. [Diagram 2] 5A and 5B are schematic diagrams illustrating gradation patterns on an intermediate transfer belt. [Diagram 3] 5 is a schematic diagram showing an example of an image adjustment pattern formed on the intermediate transfer belt when image adjustment is performed in parallel with a printing operation. FIG. [Figure 4] 5A and 5B are diagrams for explaining positions at which scraping patterns are formed on the intermediate transfer belt. [Diagram 5] FIG. 4 is a diagram showing an example of a flowchart for forming the scraping pattern. [Figure 6] FIG. 11 is a diagram showing an example of a timing chart of a cleaning operation. [Figure 7]5A to 5C are diagrams illustrating the formation of a scraping pattern according to the embodiment. [Figure 8] 11A to 11C are diagrams illustrating the scraping patterns under conditions (1) to (3) in the verification experiment. [Figure 9] FIG. 13 is a diagram for explaining the scraping patterns under conditions (4) to (6) in the verification experiment. [Figure 10] 11 is a timing chart illustrating passage of a plurality of scraping patterns through the secondary transfer nip during a cleaning operation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The best mode for carrying out the present invention will be described below with reference to the drawings. Note that a person skilled in the art can easily change or modify the present invention within the scope of the claims to create other embodiments, and these changes and modifications are included in the scope of the claims. The following description is an example of the best mode for the present invention, and does not limit the scope of the claims. In addition, the same reference numerals are used for the same or corresponding parts in each drawing, and duplicated explanations will be appropriately simplified or omitted.

[0009] FIG. 1 is a schematic diagram of a tandem type color copier (hereinafter simply referred to as a copier) which is an image forming apparatus according to this embodiment. 1, a tandem type color copier 1 (hereinafter simply referred to as the copier) as an image forming apparatus includes an original transport section 3 that transports an original to the original reading section, and an original reading section 4 that reads image information of the original. The copier also includes a paper output tray 5 on which output images are stacked, and a paper feed section 7 in which paper P as a recording medium is stored.

[0010] The copier 1 also includes registration rollers 9 (timing rollers) that adjust the timing of transport of the paper P, and an image forming unit 10 that forms toner images of each color (yellow, magenta, cyan, black). The image forming unit 10 includes, for example, photoconductor drums 11Y, 11M, 11C, and 11BK that serve as latent image carriers on which the toner images are formed, and a writing unit (exposure unit) 6. The image forming unit 10 also includes a charging device 12, a developing device 13, a cleaning unit 15, and the like that are disposed around each of the photoconductor drums 11Y, 11M, 11C, and 11BK.

[0011] The charging device 12 uniformly charges the surface of the photoconductor drum, and the writing section (exposure section) 6 emits laser light based on input image information to write an electrostatic latent image on each of the photoconductor drums 11Y, 11M, 11C, and 11BK. The developing device 13 develops the electrostatic latent image written on the photoconductor drum. The cleaning section 15 removes untransferred toner remaining on the photoconductor drum.

[0012] The copying machine 1 also includes an intermediate transfer belt 17 as an image carrier onto which a plurality of color toner images are transferred in a superimposed manner, and a primary transfer bias roller 14 that transfers the toner images formed on each of the photoconductor drums 11Y, 11M, 11C, and 11BK in a superimposed manner onto the intermediate transfer belt. The copying machine 1 also includes a secondary transfer roller 18 as a transfer member for transferring the color toner images on the intermediate transfer belt 17 onto a sheet of paper P. The copying machine 1 also includes a fixing device 20 that fixes an unfixed image on the sheet of paper P, and a toner container 28 that contains toner of each color (yellow, cyan, magenta, and black) to be supplied to the developing device 13. The copying machine 1 also includes a belt cleaning device 30 that removes toner (untransferred toner) adhering to the surface of the intermediate transfer belt 17. The copying machine 1 also includes a waste toner collection container 80 in which the untransferred toner removed by the belt cleaning device 30 or the like is collected as waste toner. The copying machine 1 also includes a control unit 90 (processor) including a CPU or the like equipped with a RAM and a ROM.

[0013] Hereinafter, the operation of the image forming apparatus during normal color image formation will be described. First, the document is transported from the document table by the transport rollers of the document transport unit 3 and placed on the contact glass of the document reading unit 4. Then, the document reading unit 4 optically reads image information of the document placed on the contact glass.

[0014] More specifically, the document reading unit 4 scans the image of the document on the contact glass while irradiating it with light emitted from an illumination lamp, and the light reflected by the document is imaged on the color sensor via a group of mirrors and a lens. The color image information of the document is read by the color sensor for each color separation light of RGB (red, green, blue), and then converted into an electrical image signal. Furthermore, the image processing unit performs processing such as color conversion processing, color correction processing, and spatial frequency correction processing based on the RGB color separation image signal, and obtains color image information of yellow, magenta, cyan, and black.

[0015] Image information for each color, yellow, magenta, cyan, and black, is transmitted to the writing unit 6. Then, laser light L based on the image information for each color is emitted from the writing unit 6 toward the surfaces of the corresponding photoconductor drums 11Y, 11M, 11C, and 11BK.

[0016] Meanwhile, the four photoconductor drums 11Y, 11M, 11C, and 11BK each rotate in the clockwise direction in FIG. 1. First, the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK are uniformly charged at the portions facing the charging device 12 (charging process). Thus, a charging potential is formed on the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK. After that, the charged surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK reach the irradiation positions of the respective laser beams.

[0017] In the writing unit 6, laser beams corresponding to the image signals are emitted from four light sources, one for each color. Each laser beam passes through a separate optical path for each color component: yellow, magenta, cyan, and black (this is the exposure process).

[0018] The laser light corresponding to the yellow component is irradiated onto the surface of the first photoconductor drum 11Y from the left side of the drawing. At this time, the laser light of the yellow component is scanned in the direction of the rotation axis of the photoconductor drum 11Y (main scanning direction) by a polygon mirror rotating at high speed. In this way, an electrostatic latent image corresponding to the yellow component is formed on the surface of the photoconductor drum 11Y after it has been charged by the charging device 12.

[0019] Similarly, the laser light corresponding to the magenta component is irradiated onto the surface of the second photoconductor drum 11M from the left on the paper, forming an electrostatic latent image corresponding to the magenta component. The laser light corresponding to the cyan component is irradiated onto the surface of the third photoconductor drum 11C from the left on the paper, forming an electrostatic latent image of the cyan component. The laser light corresponding to the black component is irradiated onto the surface of the fourth photoconductor drum 11BK from the left on the paper, forming an electrostatic latent image of the black component.

[0020] Thereafter, the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK on which the electrostatic latent images of each color are formed reach positions facing the developing devices 13. Then, toner of each color is supplied from each developing device 13 onto the photoconductor drums 11Y, 11M, 11C, and 11BK, and the latent images on the photoconductor drums 11Y, 11M, 11C, and 11BK are developed (this is the developing process).

[0021] After the development process, the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK each reach a portion facing the intermediate transfer belt 17 as an image carrier. Here, a primary transfer bias roller 14 is provided at each facing portion so as to abut against the inner circumferential surface of the intermediate transfer belt 17. Then, at the position of the primary transfer bias roller 14, the toner images of each color formed on the photoconductor drums 11Y, 11M, 11C, and 11BK are primarily transferred onto the intermediate transfer belt 17 in a sequentially overlapping manner (this is the primary transfer process).

[0022] After the transfer process, the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK each reach a position facing the cleaning unit 15. Then, the cleaning unit 15 removes and collects the untransferred toner remaining on the photoconductor drums 11Y, 11M, 11C, and 11BK (cleaning process). The untransferred toner removed and collected by the cleaning unit 15 is transported as waste toner to a waste toner collection container 80 via a transport path and collected. Thereafter, the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK pass through a charge removing unit, and a series of image formation processes on the photoconductor drums 11Y, 11M, 11C, and 11BK is completed.

[0023] Meanwhile, intermediate transfer belt 17 (image carrier) carrying a color toner image formed by superimposing and primarily transferring the toners of the respective colors on photoreceptor drums 11Y, 11M, 11C, and 11BK travels in the counterclockwise direction in FIG. 1 and reaches a position facing secondary transfer roller 18. Secondary transfer roller 18 abuts against intermediate transfer belt 17 to form a secondary transfer nip, which is a transfer nip. In this secondary transfer nip, the color toner image carried on intermediate transfer belt 17 is secondarily transferred onto paper P (secondary transfer process).

[0024] A secondary transfer bias is applied to an opposing roller 18A that faces the secondary transfer roller 18 via the intermediate transfer belt 17, and the secondary transfer roller 18 is electrically grounded. When the color toner image on the intermediate transfer belt 17 is secondarily transferred to the paper P, a transfer bias of negative polarity, which is the normal charging polarity of the toner, is applied to the opposing roller 18A, and the normally charged toner of negative polarity on the intermediate transfer belt is repulsively transferred to the paper P.

[0025] The surface of the intermediate transfer belt 17 after the secondary transfer process reaches the position of the belt cleaning device 30. The belt cleaning device 30 has a cleaning blade 31 as a cleaning member. The cleaning blade 31 removes toner (untransferred toner) adhering to the intermediate transfer belt 17. The toner removed by the cleaning blade is transported as waste toner to a waste toner collection container 80 via a transport path and collected.

[0026] Here, the paper P transported between the intermediate transfer belt 17 and the secondary transfer roller 18 (secondary transfer nip) is transported from the paper feed section 7 via the registration rollers 9 and the like. More specifically, the paper P fed by the paper feed roller 8 from the paper feed unit 7 storing the paper P passes through a conveyance guide and is then guided to the registration rollers 9. The paper P that has reached the registration rollers 9 is conveyed in a timely manner toward the secondary transfer nip.

[0027] The paper P onto which the full-color image has been transferred in the secondary transfer process is then guided to the fixing device 20. In the fixing device 20, the color image is fixed onto the paper P at the nip between a fixing roller and a pressure roller. Then, the paper P after the fixing process is discharged as an output image outside the device body by a paper discharge roller and stacked on the paper discharge tray 5, completing a series of image formation processes.

[0028] In this copying machine, a control called process control is carried out at a predetermined timing in order to stabilize image quality against environmental changes and over time. FIG. 2 is a schematic diagram for explaining a gradation pattern on the intermediate transfer belt.

[0029] The gradation patterns are made up of a plurality of toner patches having different image densities, and these gradation patterns are formed at positions (the center and both ends in the width direction) facing the optical sensor of the intermediate transfer belt 17. In the example shown in Fig. 2, gradation patterns of black, cyan, magenta, and yellow are formed from the top.

[0030] The optical sensor unit 40 has a plurality of optical sensors 40R, 40C, and 40F as adhesion amount detection means arranged at a predetermined interval in the belt width direction of the intermediate transfer belt 17. Each optical sensor outputs a signal according to the optical reflectance of the intermediate transfer belt 17 and the gradation patterns PK, PC, PM, and PY on the intermediate transfer belt 17, and detects the amount of toner adhesion. The copier 1 adjusts the image formation conditions such as the development bias Vb based on the detected toner adhesion amount.

[0031] The optical sensors 40R and 40F, which are arranged to face the width direction end regions of the intermediate transfer belt 17, are arranged outside the paper passing region. Therefore, as shown in Fig. 3, during the formation of a toner image to be transferred to paper, an image adjustment pattern is formed outside the paper passing region, and the optical sensors 40R and 40F detect the amount of toner adhesion of the image adjustment pattern. Then, based on the amount of toner adhesion detected by the optical sensors 40R and 40F, the developing bias, etc. can be adjusted to adjust the image density, etc.

[0032] The base component of the toner, silica or titanium oxide added to the toner, and other so-called external additives of the toner are transferred from the photoconductor drum 11 to the intermediate transfer belt 17. The external additives of the toner transferred to the intermediate transfer belt 17 may adhere to the intermediate transfer belt 17, causing filming on the intermediate transfer belt 17. If the surface of the photoconductor drum 11 has a lubricant application section that applies a lubricant, various components contained in the lubricant, such as boron nitride and zinc stearate, are also transferred from the photoconductor drum 11 to the intermediate transfer belt 17 in addition to the external additives of the toner. The external additives of the toner and the lubricant may interact with each other, causing the filming on the intermediate transfer belt 17 to worsen. Furthermore, at the secondary transfer nip, paper dust may be transferred from the paper P to the intermediate transfer belt 17 and adhere to the intermediate transfer belt 17, causing paper dust filming.

[0033] Such filming on the intermediate transfer belt 17 occurs when filming substances, such as various components contained in toner additives such as silica and lubricants, adhere to the intermediate transfer belt 17 due to external pressure (mainly contact pressure with the photosensitive drum). If filming occurs on the intermediate transfer belt 17, when a full solid image or halftone image is output, toner does not adhere to the areas corresponding to the filming, resulting in abnormal images such as white spots.

[0034] Furthermore, when filming occurs, the glossiness of the belt decreases. Therefore, when filming occurs in the area of ​​the intermediate transfer belt 17 facing the optical sensors 40R, 40C, and 40F, the output signal changes and it becomes impossible to properly detect the amount of the gradation pattern attached on the intermediate transfer belt. In addition, there is also a problem that the output of the optical sensor becomes unstable due to unevenness in the filming state, making it impossible to perform correct image adjustment.

[0035] Furthermore, filming may deteriorate the cleaning performance of the cleaning blade 31. In the belt width direction, gradation patterns with a large amount of adhesion per unit area are often input to the positions of the cleaning blade 31 corresponding to the positions of the optical sensors 40R, 40C, and 40F. Therefore, if filming occurs in the areas of the intermediate transfer belt 17 facing the optical sensors 40R, 40C, and 40F, there is a high risk of poor cleaning (toner slipping through) occurring when the gradation pattern is input to the cleaning blade 31.

[0036] The filming can be scraped off by toner remaining at the contact point between the cleaning blade 31 and the surface of the intermediate transfer belt 17 (hereinafter referred to as the "cleaning point"), and removed from the surface of the intermediate transfer belt 17. Specifically, the filming on the surface of the intermediate transfer belt is scraped off by the unevenness of the surface of the toner remaining at the cleaning point and the pressure of the cleaning blade 31 applied to the toner.

[0037] Therefore, in order to suppress filming on the intermediate transfer belt 17, the copying machine 1 forms a scraping pattern on the intermediate transfer belt 17 at a predetermined timing. Then, by inputting this scraping pattern to the cleaning blade 31, a sufficient amount of toner is allowed to remain at the cleaning location.

[0038] FIG. 4 is a diagram for explaining the positions at which the scraping patterns are formed on the intermediate transfer belt. FIG. 4 shows the case where three sheets are printed continuously in a normal image forming operation. As shown in FIG. 4, the formation position of the scraping pattern is as follows: 1. Position before the first sheet of paper into the secondary transfer nip 2. Position outside the width of the paper passing through the secondary transfer nip 3. Position of non-image forming area at the rear end of the paper passing through the secondary transfer nip 4. Position of the paper gap 5. Position after the final sheet passes through the secondary transfer nip Some examples include: The above 2. can be adopted in a configuration in which the width of the intermediate transfer belt is wider than the axial length of the secondary transfer roller, and the secondary transfer roller does not contact the intermediate transfer belt 17 at the position 2. This is because, in a configuration in which the secondary transfer roller 18 contacts the intermediate transfer belt 17 at the position 2, the scraping pattern formed at the position 2 is transferred to the secondary transfer roller 18. Furthermore, at the position 2 alone, filming can only be removed from the ends of the intermediate transfer belt in the width direction, so it is necessary to combine it with the strip-shaped scraping pattern that is long in the width direction of the intermediate transfer belt as described above in 1 and 3 to 5.

[0039] Regarding 3 above, it may be a position in a non-image forming area at the leading edge of the paper passing through the secondary transfer nip. Regarding 1 and 3 to 5 above, when the scraping pattern on the intermediate transfer belt passes through the secondary transfer nip, a positive bias is applied to the opposing roller 18A. By applying a positive bias to the opposing roller 18A, the scraping pattern is electrostatically attracted to the intermediate transfer belt 17, so that the scraping pattern is not transferred to the secondary transfer roller 18 or the paper P.

[0040] FIG. 5 is a diagram showing an example of a flowchart for forming the scraping pattern. When the control unit 90 receives a print command and starts driving the intermediate transfer belt 17, it starts measuring the travel distance of the intermediate transfer belt 17 (S1). When the drive of the intermediate transfer belt 17 stops, it calculates the necessary toner input amount to the cleaning blade 31 based on the filming state on the surface of the intermediate transfer belt 17 based on the measured travel distance of the intermediate transfer belt 17. Specifically, it calculates the necessary toner input amount by multiplying the travel distance of the intermediate transfer belt 17 by a coefficient. Then, it adds the calculated necessary toner input amount to calculate an integrated value of the necessary toner input amount (S2). Next, the control unit judges whether the integrated value of the necessary toner input amount exceeds a threshold value (S3). If the integrated value does not exceed the threshold value (No in S3), the flow of FIG. 5 ends. On the other hand, if the integrated value exceeds the threshold value (Yes in S3), a scraping pattern is formed during the cleaning operation as described below. Then, the toner amount of the formed scraping pattern (the amount of toner input to the cleaning blade) is subtracted from the integrated value (S4). Thus, the flow of FIG. 5 ends.

[0041] In the case of a device that detects the presence or absence of filming with an optical sensor and forms a scraping pattern, even if filming occurs outside the detection range of the optical sensor, the filming in the area of ​​the intermediate transfer belt facing the optical sensor is not removed until filming occurs in the area of ​​the intermediate transfer belt facing the optical sensor. As a result, there is a risk that the occurrence of abnormal images such as blank areas due to filming cannot be effectively suppressed.

[0042] In contrast, in this embodiment, a scraping pattern is formed based on the travel distance of the intermediate transfer belt 17. As a result, even if no filming occurs in the area of ​​the intermediate transfer belt 17 facing the optical sensor, if there is a possibility that filming occurs in other areas, a scraping pattern is formed. Therefore, filming on the intermediate transfer belt 17 can be removed more effectively than when a scraping pattern is formed based on the detection result of the optical sensor.

[0043] The above coefficient may be a fixed value, or for example, the coefficient may be changed between a color image mode and a monochrome image mode. This is because filming may deteriorate more in the color image mode than in the monochrome image mode. In the color image mode, the fixing set temperature is higher and the number of operating motors increases compared to the monochrome image mode, so the temperature inside the machine tends to rise. When the temperature inside the machine rises, the amount of stick slip of the cleaning blade 31 increases, and there is a risk that filming will deteriorate. Also, when there is a lubricant application unit for applying a lubricant to the surface of the photoreceptor drum 11, in the color image mode, the amount of lubricant that becomes a component of the filming substance adhering to the intermediate transfer belt 17 increases compared to the monochrome mode. Therefore, filming may deteriorate more in the color image mode than in the monochrome image mode.

[0044] Therefore, for example, the coefficient B in the color image mode is set to a value higher than the coefficient A in the monochrome image mode (A < B). Then, when forming an image (when driving the intermediate transfer belt), it is determined whether it is the monochrome image mode or the color image mode. In the monochrome image mode, the required toner input amount is calculated using the coefficient A, and in the color image mode, the required toner input amount is calculated using the coefficient B.

[0045] For example, when the color image mode is frequently used, the risk of filming deterioration is higher than in the monochrome image mode as described above. However, when the color image mode is frequently used, since the integrated value of the required toner input amount exceeds the threshold value at a short running distance of the intermediate transfer belt 17, the scraping pattern is formed at an early timing. On the other hand, when the monochrome image mode is frequently used, filming is less likely to deteriorate compared to the color image mode. Therefore, when the monochrome image mode is frequently used, the running distance at which the integrated value of the required toner input amount exceeds the threshold value becomes longer, and the scraping pattern is formed at a late timing.

[0046] In this way, by forming the scraping pattern based on the image mode, the scraping pattern can be formed at an appropriate timing, and wasteful toner consumption and worsening filming can be effectively suppressed.

[0047] When the copier 1 is in operation, background staining toner is continuously supplied from the developing device 13, and this background staining toner may adhere to the paper gap of the intermediate transfer belt 17. The background staining toner adhered to the paper gap adheres to the secondary transfer roller at the secondary transfer nip, and the secondary transfer roller 18 becomes stained with the toner. If the secondary transfer roller 18 becomes stained with toner in this way, when a toner image is transferred to the paper P, the toner of the secondary transfer roller 18 may adhere to the back surface of the paper P, causing back staining.

[0048] Therefore, the copying machine 1 is adapted to execute a cleaning operation for cleaning the secondary transfer roller 18. By executing this cleaning operation, the toner adhering to the secondary transfer roller 18 is moved to the intermediate transfer belt 17.

[0049] FIG. 6 is a diagram showing an example of a timing chart of the cleaning operation. As shown in FIG. 6, when the cleaning operation is performed, a negative polarity bias and a positive polarity bias are alternately applied to the opposing roller 18A to form an alternating electric field in the secondary transfer nip. By forming an alternating electric field, the toner adhering to the secondary transfer roller 18 can be efficiently cleaned by a hopping effect. Here, the hopping effect is an effect in which the toner on the secondary transfer roller 18 is easily moved to the intermediate transfer belt 17 by reciprocating between the secondary transfer roller 18 and the intermediate transfer belt 17. In this way, by forming an alternating electric field, the toner of both polarities adhering to the secondary transfer roller 18 can be moved to the intermediate transfer belt 17, and the surface of the secondary transfer roller 18 can be satisfactorily cleaned. This makes it possible to suppress back stains on the paper.

[0050] The period of negative and positive application that forms the alternating electric field is the period during which the secondary transfer roller 18 rotates once or more. In the cleaning operation that is performed before the first sheet of paper passes through the secondary transfer nip in FIG. 5, after negative and positive application are performed three times, the bias is temporarily set to zero and then a positive bias is applied again. The length of the positive bias that is applied again is adjusted according to the timing of the paper feed. It is not necessary to temporarily set the bias to zero.

[0051] Like the cleaning operation performed after the final paper in Fig. 6 has passed through the secondary transfer nip, negative application → positive application may be performed once, or negative application → positive application may be performed four or more times. Also, the bias value for the first and second negative application → positive application does not have to be constant (it may show a behavior in which the bias is amplified or attenuated stepwise). Also, if the paper interval is wide, the cleaning operation may be performed between the papers.

[0052] As described above, it is preferable that a sufficient amount of toner remains at the cleaning area, because this effectively removes filming on the surface of the intermediate transfer belt 17. However, if the amount of toner in the scraping pattern is increased and a large amount of toner is input to the cleaning area at one time, the toner may slip through, resulting in poor cleaning.

[0053] Therefore, in this embodiment, as shown in FIG. 7, a plurality of scraping patterns Kp are formed at short intervals. As shown in FIG. 7(b), each scraping pattern Kp is a belt-like pattern long in the main scanning direction, and is longer than the maximum paper passing width that the present device can convey, and extends in the main scanning direction to the opposing area of ​​the optical sensors 40R and 40F arranged opposite both ends of the intermediate transfer belt 17. This makes it possible to effectively suppress filming in the maximum paper passing width area of ​​the intermediate transfer belt 17 where the toner image to be transferred to the paper P is formed, and effectively suppress the occurrence of abnormal images such as blank areas. In addition, the scraping pattern Kp extends to the opposing area of ​​the optical sensors 40R and 40F arranged opposite both ends of the intermediate transfer belt 17. Therefore, it is possible to effectively suppress filming in the opposing portion of the intermediate transfer belt 17 to the optical sensors 40R and 40F, and it is possible to effectively detect the amount of adhesion.

[0054] The interval Sp is set so that the next scraping pattern is input before the toner forming the previous scraping pattern is completely removed from the cleaning area. The interval Sp is also set so that the amount of toner remaining at the cleaning area is equal to or less than the amount of toner that causes cleaning defects. This prevents cleaning defects and effectively prevents filming.

[0055] The verification experiments carried out by the present inventors will be described below. As shown in FIG. 8 and FIG. 9, verification experiments were carried out under conditions (1) to (6) in which the length of the scraping pattern in the surface movement direction and the number of scraping patterns were different from one another.

[0056] Condition (1) is a condition in which one scraping pattern Kp having a length in the moving direction of 32.5 mm is formed, and condition (2) is a condition in which one scraping pattern Kp having a length in the moving direction of 97.5 mm is formed. Condition (3) is a condition in which three scraping patterns Kp having a length in the moving direction of 32.5 mm are formed at intervals of 13 mm, and condition (4) is a condition in which one scraping pattern Kp having a length in the moving direction of 80 mm is formed. Condition (5) is a condition in which one scraping pattern Kp having a length in the moving direction of 200 mm is formed. Condition (6) is a condition in which three scraping patterns Kp having lengths in the moving direction of 70 mm, 60 mm, and 70 mm are formed at intervals of 80 mm. Then, cleaning performance and filming performance were evaluated under each of conditions (1) to (6).

[0057] <Cleaning performance evaluation> The cleaning performance was evaluated under the following conditions. Cleaning blade contact pressure: 20N / m - Linear speed of intermediate transfer belt: 300mm / s The cleaning ability was evaluated based on the image printed after the scraping pattern Kp was formed. When no streaky abnormal image was observed in the printed image, the cleaning ability was evaluated as "○", and when streaky abnormal image was observed in the printed image, the cleaning ability was evaluated as "×".

[0058] <Filming Evaluation> The filming property was evaluated by printing 150,000 sheets of a running chart with an image area ratio of 5%, and then forming a test pattern on the intermediate transfer belt. If no error occurred when the optical sensors 40R, 40C, and 40F detected the amount of adhesion of the test pattern, the filming property was evaluated as "good". On the other hand, if an error occurred when the optical sensors 40R, 40C, and 40F detected the amount of adhesion of the test pattern, the filming property was evaluated as "bad". As shown in the flow chart in FIG. 4, the scraping pattern Kp was calculated by calculating the toner input amount based on the travel distance of the intermediate transfer belt 17, and when the load value of the toner input amount exceeded the threshold, the image printing was temporarily stopped and the scraping pattern was formed.

[0059] The results of the verification experiment are shown in Table 1 below. [Table 1]

[0060] As shown in Table 1, under conditions (1) and (4), the cleaning performance was rated as "good", but the filming performance was rated as "bad". This is thought to be because, under the scraping patterns under conditions (1) and (4), the amount of toner input to the cleaning area at one time is small, so no toner slips through, and the cleaning performance was rated as "good". On the other hand, under conditions (1) and (4), the filming performance was rated as "bad".

[0061] As described above with reference to FIG. 5, in this embodiment, the toner amount of the formed scraping pattern (the amount of toner input to the cleaning blade) is subtracted from the cumulative value of the toner input amount, and when the cumulative value of the toner input amount exceeds a threshold value, the scraping pattern is formed. In condition (1), the amount of toner input to the cleaning blade 31 is small, so the subtraction value is small, and the frequency of the toner scraping pattern formation operation is high compared to the other conditions (2) to (6). However, since the amount of toner input to the cleaning blade in one scraping pattern formation operation is small, the filming is not sufficiently scraped off in one scraping pattern formation operation. As a result, even if the frequency of the toner scraping pattern formation operation is high, the filming on the intermediate transfer belt 17 cannot be removed well, and the filming on the intermediate transfer belt 17 worsens over time, which is considered to have resulted in the filming evaluation being "x".

[0062] As shown in Table 1, under conditions (2) and (5) in which one scraping pattern Kp with a length in the moving direction of 97.5 mm or more was formed, the cleaning performance was rated as "x." This is thought to be because a large amount of toner was input to the cleaning area at once, and the tip of the cleaning blade was unable to withstand the pressure of the toner input to the cleaning area, causing the toner to slip through, resulting in streaky abnormal images.

[0063] On the other hand, under conditions (2) and (5), the filming evaluation was "good." Because a large amount of toner is input to the cleaning blade 31, the toner can remain at the cleaning spot for a long time. This allows the filming to be removed by the toner that remains at the cleaning spot for a relatively long period of time. Therefore, it is believed that the filming on the intermediate transfer belt 17 was removed more satisfactorily than in the case of condition (1), where the filming is removed by the toner that remains at the cleaning spot intermittently. As a result, it is believed that filming on the intermediate transfer belt 17 can be suppressed over time, resulting in the filming evaluation of "good."

[0064] From the conditions (1), (2), (4), and (5), it was found that cleaning failures can be suppressed by setting at least the length of the scraping pattern Kp in the moving direction to 80 mm or less, and that filming on the intermediate transfer belt 17 over time can be suppressed by setting at least the length of the scraping pattern Kp in the moving direction to 97.5 mm or more.

[0065] As shown in Table 1, under conditions (3) and (6), the cleaning performance and filming resistance were both evaluated as "good." This is because the length of each scraping pattern Kp in the moving direction was 80 mm or less. Therefore, it is believed that the amount of toner input to the cleaning area at one time was kept below the amount of toner that would cause cleaning defects, and the cleaning blade was able to effectively block the toner at the cleaning area.

[0066] Moreover, under conditions (3) and (6), three scraping patterns are formed at a predetermined interval, and the next scraping pattern Kp is input to the cleaning spot before the toner at the cleaning spot is completely removed by the cleaning blade 31. This allows the toner filming at the cleaning spot to be continuously scraped off. Under condition (3), the total length of the three scraping patterns in the moving direction is 97.5 mm, the same as under condition (2). This allows the same amount of toner as under condition (2) to be input to the cleaning spot. Therefore, as under condition (2), the toner remaining at the cleaning spot for a certain long period of time can remove the filming on the intermediate transfer belt 17, and it is considered that the filming evaluation was "good."

[0067] In addition, under condition (6), the length of each scraping pattern in the movement direction is longer than under condition (3). Therefore, the amount of toner input to the cleaning spot at one time is greater than under condition (3). Therefore, even if the interval between the scraping patterns is longer than under condition (3), the next scraping pattern can be input to the cleaning spot before the toner at the cleaning spot is completely removed by the cleaning blade 31. Therefore, under condition (6), the filming on the intermediate transfer belt 17 can be removed by the toner that has been retained at the cleaning spot for a certain amount of time, and it is considered that the filming evaluation was "good."

[0068] On the other hand, in condition (6), if the interval between the scraping patterns is set to 13 mm as in condition (3), too much toner will remain at the cleaning points, which may result in poor cleaning. Therefore, it is necessary to set the interval between the scraping patterns according to the length of each scraping pattern in the movement direction (the amount of toner in the scraping pattern).

[0069] Condition (3) has a shorter distance from the first to the last scraping pattern than condition (6), and the period of the scraping pattern formation operation is shorter than condition (6), which reduces the downtime of the device. On the other hand, condition (6) has a larger total amount of toner input to the cleaning area in one scraping pattern formation operation than condition (3), and the toner also remains at the cleaning area for a longer period. Therefore, condition (6) has a higher filming removal effect than condition (3).

[0070] In addition, when the BN index was measured for conditions (2) and (3), the BN index was about 0.2, and for condition (1), the BN index was 0.45. The BN index is an index value indicating the amount of boron nitride, which is a component of the lubricant on the intermediate transfer belt 17. The BN index value can be obtained by using an ATR (Attenuated Total Reflection) infrared absorption spectrum. In detail, a difference spectrum is obtained between the ATR infrared absorption spectrum of the intermediate transfer belt 17 before the verification experiment and the ATR infrared absorption spectrum of the intermediate transfer belt 17 after the verification experiment. In this difference spectrum, the ratio of the peak area originating from boron nitride to the peak area originating from the intermediate transfer belt is used as the BN index.

[0071] It is preferable that the length of each scraping pattern Kp in the movement direction is shorter than the circumferential length of the secondary transfer roller 18, and the interval Sp between the scraping patterns Kp is longer than the circumferential length of the secondary transfer roller 18.

[0072] As described above, when the scraping pattern Kp passes through the secondary transfer nip, a positive bias is applied to the opposing roller 18A, and the negative toner is electrostatically attracted to the intermediate transfer belt 17, suppressing the toner from moving to the secondary transfer roller 18. However, at this time, there is a risk that the reversely charged toner of the positive scraping pattern may electrostatically move to the secondary transfer roller 18. In addition, the surface layer of the secondary transfer roller 18 is made of a foaming agent such as sponge, and many micro cells are mixed in. Therefore, there is a risk that the negatively normally charged toner of the scraping pattern may also adhere to the secondary transfer roller 18 by being scraped off by the secondary transfer roller 18 at the secondary transfer nip.

[0073] If the length of the scraping pattern Kp in the movement direction is equal to or greater than the circumferential length of the secondary transfer roller 18, the portion of the secondary transfer roller 18 that contacts the scraping pattern Kp at the secondary transfer nip will contact the scraping pattern again after one rotation of the secondary transfer roller. In this way, if the length of the scraping pattern Kp in the movement direction is equal to or greater than the circumferential length of the secondary transfer roller 18, a portion of the secondary transfer roller 18 will be in continuous contact with the scraping pattern, and there is a risk that toner contamination in that portion will be worse than in other portions.

[0074] Even if the length of the scraping pattern Kp in the movement direction is made shorter than the circumferential length of the secondary transfer roller 18, if the interval Sp of the scraping pattern Kp is shorter than the circumferential length of the secondary transfer roller 18, there will be a portion of the secondary transfer roller 18 that is in continuous contact with the scraping pattern. Therefore, there is a risk that the toner contamination in that portion will be worse than in other portions.

[0075] By making the length of each scraping pattern Kp in the moving direction shorter than the circumferential length of the secondary transfer roller 18 and making the interval Sp between the scraping patterns Kp longer than the circumferential length of the secondary transfer roller 18, it is possible to prevent the secondary transfer roller 18 from having a portion that continuously comes into contact with the scraping patterns Kp. As a result, the portion that comes into contact with the scraping patterns Kp at the secondary transfer nip comes into contact with the intermediate transfer belt 17 after one rotation, and a portion of the toner that adheres to the secondary transfer roller 18 when it comes into contact with the scraping patterns Kp can be transferred to the intermediate transfer belt 17. Therefore, toner contamination of the secondary transfer roller can be suppressed compared to when the length of the scraping patterns Kp in the moving direction is set to be equal to or greater than the circumferential length of the secondary transfer roller 18 or when the interval Sp between the scraping patterns Kp is set to be equal to or less than the circumferential length of the secondary transfer roller 18.

[0076] In this embodiment, multiple scraping patterns Kp are formed at a predetermined interval (an interval at which the amount of toner remaining at the cleaning area does not fall below a predetermined amount), so the period of the scraping pattern formation operation is long. Therefore, if the cleaning operation and the scraping pattern formation operation are performed at different times, the travel distance of the intermediate transfer belt 17 may be extended, shortening the life of the intermediate transfer belt 17. In addition, the number of times the device is downtimed may increase.

[0077] Therefore, in this embodiment, as shown in FIG. 10, the roller is caused to pass through the secondary transfer nip when the positive bias is applied in the cleaning operation. In this embodiment, as described above, an alternating electric field is formed in the secondary transfer nip to clean the toner adhering to the secondary transfer roller 18 by the hopping effect. As shown in FIG. 10, the polarity of the alternating electric field is switched at a timing shorter than the paper-present section in the secondary transfer nip. Therefore, by passing the scraping pattern while a positive bias is being applied in this alternating electric field, the next scraping pattern can be input to the cleaning spot before the toner remaining in the cleaning spot is completely removed. This allows the toner remaining in the cleaning spot to continue for a certain long time to remove filming on the intermediate transfer belt, and filming can be suppressed over time.

[0078] As shown in FIG. 10, the positive bias and the negative bias are applied for at least one revolution of the secondary transfer roller. Therefore, the length of each scraping pattern Kp in the moving direction can be made shorter than the circumference of the secondary transfer roller 18, and the interval Sp between the scraping patterns Kp can be made longer than the circumference of the secondary transfer roller 18, so that toner staining of the secondary transfer roller and back staining of the paper can be suppressed. Even if the scraping pattern passes through the secondary transfer nip when the positive bias is applied, the toner of negative polarity attached to the secondary transfer roller can be electrostatically attached to the intermediate transfer belt (scraping pattern). Therefore, the scraping pattern has almost no effect on cleaning of the secondary transfer roller.

[0079] Even if the scraping pattern is passed when the zero bias is applied in the cleaning operation, the scraping pattern Kp is not transferred to the secondary transfer roller 18. However, unlike when a positive bias is applied, the toner of the scraping pattern is not electrostatically attracted to the intermediate transfer belt 17. Therefore, at the secondary transfer nip, the toner may be scraped off by the secondary transfer roller 18, and more toner may adhere to the secondary transfer roller 18, which may worsen the toner stain on the secondary transfer roller 18. Therefore, it is not preferable to pass the scraping pattern when the zero bias is applied in the cleaning operation.

[0080] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the spirit of the present invention described in the claims, unless otherwise specifically limited in the above description.

[0081] The above description is merely an example, and each of the following aspects provides unique effects. (Aspect 1) In an image forming apparatus including an image carrier such as an intermediate transfer belt 17, a transfer member such as a secondary transfer roller 18 that contacts the image carrier to form a transfer nip such as a secondary transfer nip, a bias application means that applies a transfer bias to the transfer nip for transferring a toner image on the image carrier to a recording medium such as paper P, and a cleaning member such as a cleaning blade 31 that cleans the surface of the image carrier, the apparatus has a cleaning operation that applies a reverse polarity bias such as a positive bias having a polarity (positive) opposite to the polarity (negative) of at least the transfer bias to the transfer nip, moves deposits on the transfer member to the image carrier, and cleans the transfer member, and forms a plurality of toner image patterns such as a scraping pattern Kp that are not transferred to the recording medium at a predetermined interval, the length of the toner image patterns in the surface movement direction of the image carrier being shorter than the circumferential length of the transfer member, and the interval between the toner image patterns being equal to or longer than the circumferential length of the transfer member, and the plurality of toner image patterns are caused to pass through the transfer nip when the reverse polarity bias is applied in the cleaning operation. To prevent filming, it is preferable to increase the amount of toner in the toner image pattern and to increase the amount of toner input to the cleaning unit, but if a large amount of toner is input to the cleaning unit at once, there is a risk of poor cleaning. In addition, when the toner image pattern passes through the transfer nip, the toner constituting this toner image pattern may adhere to the transfer member. When the toner image is transferred to the recording medium at the transfer nip, the toner adhered to the transfer member may adhere to the back surface of the recording medium, causing back staining that soils the back surface of the recording medium. In the first aspect, a plurality of toner image patterns that are not transferred to a recording medium are formed at a predetermined interval, and the plurality of toner image patterns are passed through the transfer nip while a reverse polarity bias that is the opposite polarity to the transfer bias during the cleaning operation is applied. This reduces the amount of toner input to the cleaning member at one time, and allows an amount of toner that can prevent filming to be input to the cleaning member during the cleaning operation. This makes it possible to suppress the occurrence of cleaning defects and suppress filming. In addition, since the plurality of toner image patterns pass through the transfer nip while the reverse polarity bias is applied in the cleaning operation, the toner of the toner image patterns is prevented from moving to the transfer member, and back surface staining can also be suppressed. Furthermore, the number of times the apparatus is down can be reduced compared to when a plurality of toner image patterns are formed at predetermined intervals at a timing separate from the cleaning operation. In addition, the length of the toner image pattern in the surface movement direction of the image carrier is made shorter than the circumferential length of a transfer member such as the secondary transfer roller 18, and the interval Sp between the toner image patterns is made equal to or greater than the circumferential length of the transfer member, so that the portion of the transfer member that comes into contact with the toner image pattern at the transfer nip can come into contact with the image carrier after one rotation. This allows the toner of the toner image pattern that has adhered to the transfer member at the transfer nip to move to the surface of the image carrier after one rotation of the transfer member, thereby preventing contamination of the transfer member. This further prevents back surface contamination.

[0082] (Aspect 2) In aspect 1, an adhesion amount detection means such as optical sensors 40R, 40F are arranged at both ends of the main scanning direction of an image carrier such as intermediate transfer belt 17, and detect the toner adhesion amount of a toner image, and a toner image pattern such as scraping pattern Kp is a band-shaped pattern that is equal to or longer than the length in the main scanning direction from the adhesion amount detection means at one end in the main scanning direction to the adhesion amount detection means at the other end in the main scanning direction. According to this, as described in the embodiment, it is possible to effectively suppress filming in the maximum paper passing width region of the image carrier such as the intermediate transfer belt on which the toner image to be transferred to the recording medium such as the paper P is formed, and to effectively suppress the occurrence of abnormal images such as blank areas. Also, it is possible to effectively suppress filming in the facing regions of the adhesion amount detection means such as the optical sensors 40R and 40F arranged to face each other at both ends of the image carrier, and to effectively detect the adhesion amount.

[0083] (Aspect 3) In the embodiment 1 or 2, the cleaning operation involves forming an alternating bias in the transfer nip to move any deposits adhering to a transfer member such as the secondary transfer roller 18 to the image carrier, and one scraping pattern passes through the transfer nip while a reverse polarity bias is being applied when the alternating bias is applied. According to this, as described in the embodiment, a plurality of scraping patterns can be formed at predetermined intervals, and the scraping patterns can pass through the transfer nip while the reverse polarity bias is being applied in the cleaning operation. Furthermore, the deposits adhering to the transfer member can be efficiently cleaned off by the hopping effect. [Explanation of symbols]

[0084] 1: Copying machine (image forming device) 17: Intermediate transfer belt (image carrier) 18: Secondary transfer roller (transfer member) 18A: Opposing roller 30: Belt cleaning device 31: Cleaning blade (cleaning member) 40: Optical sensor unit 40C: Optical sensor 40F: Optical sensor 40R: Optical sensor Kp: Scraping pattern P:Paper [Prior art documents] [Patent documents]

[0085] [Patent Document 1] JP 2016-020970 A

Claims

1. An image carrier; a transfer member that contacts the image carrier to form a transfer nip; a bias applying unit that applies a transfer bias to the transfer nip in order to transfer the toner image on the image carrier to a recording medium; a cleaning member for cleaning the surface of the image carrier, a cleaning operation for applying a reverse polarity bias, which is reverse to the polarity of at least the transfer bias, to the transfer nip, and moving any deposits on the transfer member to the image carrier, thereby cleaning the transfer member; forming a plurality of toner image patterns that are not transferred onto the recording medium at predetermined intervals; a length of the toner image pattern in a surface movement direction of the image carrier is shorter than a circumferential length of the transfer member, and an interval between the toner image patterns is equal to or longer than the circumferential length of the transfer member; an image forming apparatus including: passing a plurality of said toner image patterns through said transfer nip when said reverse polarity bias is applied in said cleaning operation;

2. 2. The image forming apparatus according to claim 1, a toner adhesion amount detection unit disposed on both ends of the image carrier in a main scanning direction and configured to detect a toner adhesion amount of the toner image; the toner image pattern is a belt-shaped pattern having a length in the main scanning direction greater than or equal to a length from one end of the adhesion amount detection means in the main scanning direction to the other end of the adhesion amount detection means in the main scanning direction;

3. 2. The image forming apparatus according to claim 1, the cleaning operation is to apply an alternating bias to the transfer nip to move the deposit adhering to the transfer member to the image carrier; an image forming apparatus comprising: a scraping pattern passing through said transfer nip while a bias of a reverse polarity is being applied during application of said alternating bias;

Images