Image forming apparatus

Abstract

To provide an image forming apparatus that comprises a scraper that removes an attachment attached to the surface of an intermediate transfer belt, and that can remove a deposit deposited on a contact part of the scraper with a simple configuration.SOLUTION: A deposit deposited on a nip part between the surface of an intermediate transfer body and a cleaning scraper and a deposit deposited on a nip part between the surface of the intermediate transfer body and a cleaning member, can be efficiently removed by performing reverse rotation control, and scratches generated on the surface of the intermediate transfer body can be prevented.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus equipped with a cleaning blade that contacts and cleans the surface of an image bearing member, and a scraper that contacts and cleans the surface of an image bearing member. [Background technology]

[0002] Conventional electrophotographic image forming apparatuses are equipped with a cleaning device that removes (cleans) residual toner adhering to the surface of an image carrier, such as a photoreceptor or intermediate transfer belt, after a toner image has been transferred to a recording sheet. The cleaning device has a cleaning member that comes into contact with the surface of the image carrier to remove the residual toner, and also cleans off external additives added to the toner and paper dust peeled off from the recording sheet that are adhering to the surface of the image carrier, in addition to the toner.

[0003] The external additives usually have a smaller particle size than toner and are therefore difficult to clean. Furthermore, if the external additives cannot be sufficiently removed, filming, in which the external additives adhere to the surface of the image carrier, may occur. If the filming occurs, when a blade-shaped cleaning member (cleaning blade) is used, the frictional resistance between the image carrier and the cleaning blade increases, which may cause the tip of the blade to curl up and result in poor cleaning.

[0004] Furthermore, if the external additives and paper dust cannot be sufficiently removed, the charged potential on the surface of the image carrier will decrease, causing transfer failures and image defects. Furthermore, if the paper dust gets into the contact area between the cleaning blade and the image carrier, the paper dust may become trapped in the contact area, leading to toner passing through the part where the paper dust is trapped, resulting in poor cleaning.

[0005] Patent Document 1 discloses a cleaning device that cleans the surface of an endless belt. The endless belt is cleaned by a cleaning brush that rotates while in contact with the surface of an image carrier and collects toner from the surface of the image carrier. After that, a scraper collects any remaining toner, paper dust, etc. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-347864 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the case of the configuration described in Patent Document 1, a scraper with high hardness is used, and the belt surface may be scraped by the rubbing of the cleaning member, generating abrasion powder. This abrasion powder may then get caught in the contact area of ​​the scraper and damage the belt surface.

[0008] Therefore, an object of the present invention is to provide an image forming apparatus equipped with a scraper that removes deposits adhering to the surface of an image carrier, which is capable of removing deposits that have accumulated at the scraper contact portion with a simple configuration. [Means for solving the problem]

[0009] The above object can be achieved by an image forming apparatus according to the present invention. In summary, the image forming apparatus includes a rotatable image carrier that carries a toner image, a transfer member that transfers the toner image formed on the image carrier to a recording material, a cleaning blade that contacts the image carrier at a first contact portion and cleans toner remaining on the image carrier, a scraper that contacts the image carrier at a second contact portion downstream of the first contact portion in the rotation direction of the image carrier, a drive source that drives the image carrier, and a control unit that controls the drive source to perform a reverse rotation operation to rotate the image carrier in the reverse direction, wherein the control unit controls the drive source when performing the reverse rotation operation so that a moving distance of the image carrier when rotated in the reverse direction is longer than a circumferential distance L of the image carrier between the first contact portion and the second contact portion. [Effects of the Invention]

[0010] According to the present invention, an image forming apparatus equipped with a scraper that removes deposits adhering to the surface of an image carrier can be provided, which is capable of removing deposits that have accumulated at the scraper contact portion with a simple configuration. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view of an intermediate transfer belt cleaning device according to the present embodiment. [Figure 3] FIG. 10 is an explanatory diagram illustrating how the surface of the intermediate transfer belt is scratched. [Figure 4] 10 is an explanatory diagram illustrating how the reverse rotation operation removes the abrasion powder trapped in the cleaning nip R portion. FIG. [Figure 5] FIG. 2 is a control flowchart of the present embodiment. [Figure 6] FIG. 2 is a control block diagram of the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Example 1] 1. Overall configuration and operation of the image forming apparatus 1 is a schematic cross-sectional view of an image forming apparatus 100 according to this embodiment. The image forming apparatus 100 according to this embodiment is a tandem laser beam printer that employs an intermediate transfer system and is capable of forming full-color images using an electrophotographic system.

[0013] Image forming apparatus 100 has a plurality of image forming units (stations), namely, first, second, third, and fourth image forming units PY, PM, PC, and PK. The first, second, third, and fourth image forming units PY, PM, PC, and PK are arranged linearly in this order along the rotation direction of intermediate transfer belt 7 (described later), and form images of yellow (Y), magenta (M), cyan (C), and black (K), respectively.

[0014] In addition, when there is no need to distinguish between elements having similar functions and configurations provided for each image forming unit PY, PM, PC, and PK, the suffixes Y, M, C, and K indicating that the element is for one of the colors will be omitted and the elements will be described generally. Also, elements for each color may be distinguished by prefixing them with Y, M, C, and K.

[0015] The image forming unit P has a rotatable drum-type (cylindrical) electrophotographic photosensitive member (photosensitive drum) 1. The photosensitive member 1, which serves as an image carrier, is driven to rotate in the direction of arrow R1 in the figure. The following devices are arranged around the photosensitive member 1 in this order: First, a charging roller 2, which is a roller-type charging member serving as charging means, is arranged; Next, an image exposure device (laser scanner) 3, which serves as image exposure means, is arranged; Next, a developing device 4, which serves as developing means, is arranged; Next, a primary transfer roller 5, which is a roller-type primary transfer member serving as primary transfer means, is arranged; Next, a cleaning device 6, which serves as photosensitive member cleaning means, is arranged.

[0016] The image forming apparatus 100 also includes an intermediate transfer belt (intermediate transfer belt) 7, an endless belt serving as another image carrier, facing the photoconductors 1 of all image forming stations P. The intermediate transfer belt 7 is an example of a moving body that is cleaned by a cleaning blade 82, moves in the direction of arrow R2 in the figure, carries a toner image to be transferred to a recording material, and conveys it to a contact point with the recording material (secondary transfer station T2). The intermediate transfer belt 7 is stretched by a plurality of support rollers 71-74 and is given a predetermined tension. When a drive roller 71, one of the support rollers, is driven to rotate, the driving force is transmitted to the intermediate transfer belt 7, causing it to rotate in the direction of arrow R2 in the figure. The above-mentioned primary transfer rollers 5Y, 5M, 5C, and 5K are disposed on the inner circumferential surface (back surface) of the intermediate transfer belt 7, at positions facing the respective photoconductors 1Y, 1M, 1C, and 1K. The primary transfer roller 5 is pressed against the photosensitive member 1 via the intermediate transfer belt 7, forming a primary transfer portion (primary transfer nip) T1 where the intermediate transfer belt 7 and the photosensitive member 1 come into contact. A secondary transfer roller 9, a roller-shaped secondary transfer member serving as secondary transfer means, is disposed on the outer circumferential surface (surface) of the intermediate transfer belt 7, facing a drive roller 71, one of the multiple support rollers. The secondary transfer roller 9 forms a secondary transfer portion (secondary transfer nip) T2 where the intermediate transfer belt 7 and the secondary transfer roller 9 come into contact. A belt cleaning device 8, serving as intermediate transfer cleaning means, is disposed on the outer circumferential surface of the intermediate transfer belt 7, facing a tension roller 74.

[0017] The intermediate transfer belt 7 will now be described in detail. The intermediate transfer belt 7 has a base layer and a surface layer provided on the outer peripheral surface of the base layer. The surface layer is a coating layer formed directly on the base layer to ensure toner releasability. In other words, the intermediate transfer belt 7 has a two-layer structure. However, the surface layer may also have a coating layer and an adhesive layer that bonds the coating layer to the base layer. In other words, the intermediate transfer belt 7 may have a three-layer structure.

[0018] [Base layer] First, the base layer will be described. The base layer contains one of the following resins: polyimide (PI), polyamide (PA), polyphenylene sulfide (PPS), polyetherimide (PEI), and polyether ether ketone (PEEK). The base layer is made by dispersing an appropriate amount of conductive filler such as carbon or an ionic conductive material in one of these resins. The surface resistivity α of the base layer alone is 1.0×10Ω / □≦α≦1.0×10Ω / □, and preferably 6.3×10Ω / □≦α≦3.2×10Ω / □. The thickness D of the base layer satisfies 30μm≦D≦100μm.

[0019] [surface] Next, the surface layer will be described. The surface layer contains at least a binder resin and perfluoropolyether (PFPE). That is, the surface layer is mainly composed of a binder resin, perfluoropolyether (PFPE), a dispersant, and other additives.

[0020] The binder resin contained in the surface layer is used to disperse the PFPE, ensure adhesion to the base layer, and ensure mechanical strength characteristics. Examples of the binder resin in this embodiment include styrene resin, acrylic resin, methacrylic resin, epoxy resin, polyester resin, polyether resin, silicone resin, and polyvinyl butyral resin. Mixtures of these resins can also be used. Among the above binder resins, methacrylic resin or acrylic resin (hereinafter, methacrylic resin and acrylic resin are collectively referred to as acrylic resin) are particularly preferred.

[0021] Perfluoropolyether is an oligomer or polymer having a perfluoroalkylene ether as a repeating unit. Examples of repeating units of perfluoroalkylene ether include perfluoromethylene ether, perfluoroethylene ether, and perfluoropropylene ether. The surface layer preferably contains a dispersant for dispersing the perfluoropolyether. The inclusion of such a dispersant can further stabilize the dispersion state of the PFPE in the surface layer. Dispersants are compounds having a perfluoroalkyl chain and a hydrocarbon affinity (compounds having both a portion with high and a portion with low affinity for fluorine), and surfactants, amphiphilic block copolymers, and amphiphilic graft copolymers are preferably used. While the intermediate transfer belt 7 in this embodiment has two or more layers, a single-layer intermediate transfer belt 7 may also be used.

[0022] Furthermore, the image forming apparatus 100 includes a feeding means for the recording material M, and a fixing device 10 as a fixing means for fixing the toner image onto the recording material M.

[0023] During image formation, the surface of the rotating photoreceptor 1 is charged almost uniformly to a predetermined potential of a predetermined polarity (negative in this embodiment) by the charging roller 2 to which a charging bias is applied. Note that, in the direction of rotation of the photoreceptor 1, minute gaps are formed between the photoreceptor 1 and the charging roller 2 on the upstream and downstream sides of the contact point between the photoreceptor 1 and the charging roller 2. The charging roller 2 charges the surface of the photoreceptor 1 by discharge occurring in at least one of the gaps on the upstream and downstream sides.

[0024] The charged surface of the photoreceptor 1 is image-exposed (scanned) by an image exposure device 3 with a laser beam (not shown) based on image information, forming an electrostatic latent image (electrostatic image). The electrostatic latent image formed on the photoreceptor 1 is developed (visualized) as a toner image by a developing device 4 using toner as a developer. The developing device 4 has a developing roller 41 as a developer carrier that carries the toner and transports it to an area facing the photoreceptor 1. During development, an oscillating voltage consisting of a superimposed DC voltage and an AC voltage is applied to the developing roller 41 as a development bias from a developing power supply (not shown) that serves as a development bias application means. In this embodiment, a toner image is formed by image area exposure and reversal development. That is, toner charged with the same polarity as the charge polarity of the photoreceptor 1 adheres to the exposed area on the photoreceptor 1, where the absolute value of the potential has been reduced by exposure after being approximately uniformly charged.

[0025] The toner image formed on the photoconductor 1 is transferred (primary transfer) onto the intermediate transfer belt 7 at the primary transfer portion T1 by a primary transfer roller to which a primary transfer bias is applied. In the rotation direction of the photoconductor 1, the photoconductor 1 and the intermediate transfer belt 7 come into contact, and the position where the toner image is transferred from the photoconductor 1 to the intermediate transfer belt 7 is the primary transfer position (primary transfer portion) T1. For example, when a full-color image is formed, the toner images of yellow, magenta, cyan, and black formed on each photoconductor 1 are transferred to the intermediate transfer belt 7 so as to be superimposed at each primary transfer portion T1. The toner image formed on the intermediate transfer belt 7 is transferred (secondary transfer) onto the recording material M at the secondary transfer portion T2 by a secondary transfer roller 9 to which a secondary transfer bias is applied. The recording material M is sent out from a cassette 12, which is a storage section, by a pickup roller 13, transported by a pair of transport rollers 14, and transported to the secondary transfer section T2 in synchronization with the toner image on the intermediate transfer belt 7 by a pair of registration rollers 16.

[0026] The recording material M onto which the toner image has been secondarily transferred is transported to the fixing device 10, where it is heated and pressurized. This fixes the toner image onto the recording material M. The temperature of the fixing device is determined by an environmental temperature sensor (not shown) and the setting of the paper type. Generally, if the process speed is the same, the lower the environmental temperature and the greater the basis weight of the set paper type, the higher the temperature of the fixing device is set. In this embodiment, the paper types include plain paper 1, plain paper 2, plain paper 3, etc., and each has a basis weight of 64 to 75 g / m 2 , 76~90g / m 2 , 91~105g / m 2 The temperatures of the fixing units are set to 190° C., 200° C., and 210° C., respectively, at an ambient temperature of 23° C. After passing through the fixing units, the recording material M is conveyed to the paper discharge tray 11, and the series of image forming processes is completed.

[0027] Although plain paper, synthetic resin sheets, envelopes, etc. are used as the recording material M, in this embodiment, the recording material M will be described as plain paper. Sheets are selectively fed and conveyed one by one by a paper feed roller 13 from a cassette 12 detachably disposed at the bottom of the main body of the image forming apparatus 100.

[0028] After the primary transfer step, the surface of the photosensitive drum 1 is cleaned by a drum cleaning device 6. The drum cleaning device 6 uses a cleaning blade (not shown) arranged in contact with the photosensitive drum 1 to scrape and remove deposits such as primary transfer residual toner from the surface of the rotating photosensitive drum 1, and collects them in a collection container.

[0029] Furthermore, the surface of the intermediate transfer belt 7 after the secondary transfer step is cleaned by a belt cleaning device 8. The belt cleaning device 8 uses a cleaning blade 82 arranged in contact with the intermediate transfer belt 7 to scrape and remove deposits such as secondary transfer residual toner (hereinafter referred to as transfer residual toner) from the surface of the intermediate transfer belt 7, and collects the toner in a collection container.

[0030] The toner consumed is replenished from the toner bottle 16 to the developing device 4 .

[0031] 2. Belt cleaning device 2 is a schematic cross-sectional view of the belt cleaning device 8 in this embodiment, showing a cross section that is approximately perpendicular to the direction of movement of the surface of the intermediate transfer belt 7.

[0032] The belt cleaning device 8 has a collection container (casing) 81 having an opening 81a on the side of the intermediate transfer belt 7. A cleaning blade 82 and a cleaning scraper 86 are attached to the opening 81a of the collection container 81 via a support member 83. The cleaning blade 82 and the cleaning scraper 86 are arranged along a direction (width direction of the intermediate transfer belt 7) that is substantially perpendicular to the moving direction R2 of the surface of the intermediate transfer belt 7. The cleaning blade 82 and the cleaning scraper 86 are plate-like members of a predetermined thickness and having predetermined lengths in the longitudinal direction and in the lateral direction perpendicular to the longitudinal direction.

[0033] In this embodiment, the cleaning blade 82 is formed of urethane rubber as an elastic material. One end of the cleaning blade 82 in the short side direction is fixed to a support member 83, and the support member 83 is fixed to a collection container 81. An outer edge portion 82a of the free end of the cleaning blade 82 in the short side direction is in contact with the intermediate transfer belt 7 in the counter direction to the transport direction of the intermediate transfer belt 7. In other words, the cleaning blade 82 is in contact with the surface of the intermediate transfer belt 7 with the free end facing upstream in the movement direction of the surface of the intermediate transfer belt 7 during image formation. The contact portion between the cleaning blade 82 and the intermediate transfer belt 7 is a cleaning nip (cleaning portion) Q, which serves as a first contact portion.

[0034] The cleaning scraper 86 is disposed downstream of the cleaning blade 82 and is made of a polyester resin material. The cleaning scraper 86 abuts against the surface of the intermediate transfer belt 7 in the counter direction relative to the transport direction of the intermediate transfer belt 7. That is, the cleaning blade 82 abuts against the surface of the intermediate transfer belt 7 with the tip of its free end facing upstream in the direction of movement of the surface of the intermediate transfer belt 7 during image formation. The abutment portion between the cleaning blade 82 and the intermediate transfer belt 7 is a cleaning nip (cleaning portion) R, which serves as a second abutment portion. In this embodiment, a polyester-based material is used, but any material harder than the cleaning blade may be used, such as a metal material, an ABS material, or a PET material.

[0035] A contact member, a scooping sheet 84, is attached to the opening 81 of the collection container 81 upstream of the cleaning blade 82 in the surface movement direction of the intermediate transfer belt 7. The scooping sheet 84 is a sheet-like member of a predetermined thickness, disposed in a direction substantially perpendicular to the surface movement direction of the intermediate transfer belt 7, and having predetermined lengths in both the longitudinal direction and the lateral direction perpendicular to the longitudinal direction. In this embodiment, the scooping sheet 84 is formed from a flexible plastic sheet. One end of the scooping sheet 84 in the lateral direction is fixed to and supported by the collection container 81. The tip of the free end of the scooping sheet 84 in the lateral direction contacts the intermediate transfer belt 7. The tip of the free end of the scooping sheet 84 contacts the intermediate transfer belt 7 with the free end facing downstream in the surface movement direction of the intermediate transfer belt 7 during image formation. The scooping sheet 84 drops the toner scraped off by the cleaning blade 82 into the collection container 81 and prevents the toner from flowing back toward the intermediate transfer belt 7. Further, within the collection container 81, a conveying screw 85 is disposed for conveying the collected toner in the longitudinal direction and discharging it into a collected toner box (not shown) separately provided in the image forming apparatus 100.

[0036] 3. Developer The developing device 4 develops the electrostatic image on the photoreceptor 1 using a two-component developer made by mixing carrier (magnetic) and toner (non-magnetic). The developer used was a mixture of carrier and toner in a weight ratio of 91:9 (toner concentration: 9%). The total weight of the initial developer contained in the developing device 4 was 208 g.

[0037] The carrier is made of ferrite particles coated with silicone resin, and has a saturation magnetization of 24 Am2 / kg in an applied magnetic field of 240 kA / m. It also has a resistivity of 1×107 Ω·cm to 1×108 Ω·cm in an electric field strength of 3000 V / cm, and a weight-average particle size of 50 μm.

[0038] The toner is composed of at least a binder, a colorant, and a charge control agent. Here, a styrene-acrylic resin is used as the binder resin. However, styrene-based, polyester-based, polyethylene-based, and other resins can also be used. The colorant may be a variety of pigments or dyes, and one type of colorant may be used alone or multiple types may be used in combination. The charge control agent may contain a reinforcing charge control agent as needed. Examples of reinforcing charge control agents that can be used include nigrosine dyes and triphenylmethane dyes.

[0039] The toner contains wax. The wax is contained to improve fixability and release from the fixing member during fixing. Examples of wax that can be used include paraffin wax, carnauba wax, and polyolefin, which are kneaded and dispersed in a binder resin. In this example, a resin containing a binder, colorant, charge control agent, and wax kneaded and dispersed therein was pulverized using a mechanical pulverizer. The melting point of the wax used in this example was 100°C or less.

[0040] The toner contains an external additive. Examples of the external additive include amorphous silica that has been hydrophobized, or inorganic oxide particles such as titanium oxide or titanium compounds. These particles are added to the toner to adjust the powder fluidity and charge amount of the toner. The particle diameter of the external additive particles is preferably 1 nm or more and 100 nm or less. In this example, 0.5 wt% of titanium oxide with an average particle diameter of 50 nm was added, and 0.5 wt% and 1.0 wt% of amorphous silica with average particle diameters of 2 nm and 100 nm, respectively, were added.

[0041] The particle size of the toner having the above-mentioned composition was measured using a powder particle size image analyzer FPIA-3000 manufactured by Sysmex Corporation, and the weight average particle size was found to be 6.6 μm.

[0042] 4. Image defects due to scratches on the intermediate transfer belt surface Next, image defects caused by scratches on the surface of the intermediate transfer belt will be described with reference to FIG. 3. When the cleaning blade 82 performs a cleaning operation, slight vibrations occur, creating a small gap between the intermediate transfer belt 7 and the cleaning blade 82. Contaminants (toner, paper dust, etc.) on the intermediate transfer belt may slip through this gap and pass through the cleaning blade 82. As shown in FIG. 3(a), the toner and paper dust that have slipped through are collected by the cleaning scraper 86. Immediately after initial use of the main body, there is nothing present in the cleaning nip R between the intermediate transfer belt 7 and the cleaning scraper 86.

[0043] If paper continues to be passed thereafter, as shown in FIG. 3(b), because the cleaning scraper 86 is made of a relatively hard material, the surface of the intermediate transfer belt is scraped away by the friction between the intermediate transfer belt 7 and the cleaning scraper 86. As a result, abrasion dust from the intermediate transfer belt 7 becomes trapped in the cleaning nip R. If the intermediate transfer belt 7 continues to rotate with abrasion dust from the intermediate transfer belt 7 trapped in the nip R, the following problems may occur. Specifically, the abrasion dust trapped in the nip continuously forms scratches, resulting in localized surface scratches of about several microns in size on the intermediate transfer belt 7. Furthermore, these surface scratches may result in poor cleaning or poorly transferred images.

[0044] 5. Efficient discharge control of abrasive particles caught in the cleaning nip R section (reverse rotation control) Next, a means for removing the abrasion powder of the intermediate transfer belt 7 caught in the cleaning nip R in this embodiment will be described with reference to FIG.

[0045] 4(a), if paper continues to pass through, the surface of the intermediate transfer belt 7 is scraped away by the friction between the intermediate transfer belt 7 and the cleaning scraper 86, and the scraped powder from the intermediate transfer belt 7 becomes caught in the nip at the cleaning nip R. As mentioned above, if the intermediate transfer belt 7 continues to rotate with the scraped powder from the intermediate transfer belt 7 caught in the nip at the cleaning nip R, there is a risk of local scratches or poor cleaning.

[0046] Therefore, as shown in FIG. 4(b), reverse rotation control of the intermediate transfer belt 7 is performed to avoid surface scratches on the intermediate transfer belt 7. In this embodiment, the reverse rotation control is performed so that the reverse rotation operating distance (movement distance) is longer than the belt circumferential distance L between the cleaning scraper 86 and the cleaning blade 82. In other words, the reverse rotation operation is performed so that the reverse rotation operating distance is equal to or greater than the circumferential distance L of the intermediate transfer belt 7 between the cleaning nip Q portion, which is the first contact portion, and the cleaning nip R portion, which is the second contact portion. In this way, the abrasion powder sandwiched in the cleaning nip R portion is caused to collide with the cleaning nip Q portion between the cleaning blade 82 and the intermediate transfer belt 7, and can be collected or the abrasion powder shape can be broken down.

[0047] Here, the effect of performing reverse rotation control with a reverse rotation operating distance longer than the belt circumferential distance L between the cleaning scraper 86 and the cleaning blade 82 will be described. When the reverse rotation operation removes the abrasion dust that was sandwiched in the cleaning nip R, the abrasion dust adheres or adheres to the intermediate transfer belt 7 with strong force. Consider a case where the reverse rotation operating distance is less than the belt circumferential distance L between the cleaning scraper 86 and the cleaning blade 82. In this case, the abrasion dust that was once sandwiched in the cleaning nip R is removed from the nip by the reverse rotation operation, but it again enters the cleaning scraper nip R without changing its shape at all. As a result, there is a possibility that the abrasion dust will be sandwiched in the cleaning nip R again, which limits the effectiveness of removing the abrasion dust.

[0048] Next, as shown in FIG. 4(c), consider the case where the reverse rotation distance is equal to or greater than the belt circumferential distance L between the cleaning scraper 86 and the cleaning blade 82. In this case, during the reverse rotation, the abrasive particles that were caught in the cleaning nip R collide with the cleaning nip Q and fall off the intermediate transfer belt 7 or change shape. Then, the abrasive particles that remain attached to the intermediate transfer belt 7 but do not fall off fall off or are separated from the intermediate transfer belt 7 by the forward rotation after the reverse rotation (A). Furthermore, if the abrasive particles enter the cleaning scraper 86 again without falling off or being separated, they are cleaned and collected without being caught again in the cleaning nip R of the cleaning scraper 86 (B).

[0049] For this reason, it is preferable to periodically perform reverse rotation control over a distance longer than the belt circumferential distance L between the cleaning scraper 86 and the cleaning blade 82. By doing so, the abrasive powder caught in the cleaning nip R portion is caused to collide with the cleaning blade 82 and is ultimately collected by either the cleaning blade 82 or the cleaning scraper 86, thereby making it possible to prevent scratches from being formed on the intermediate transfer belt 7.

[0050] 6. Details of the Control Mode of this Example Fig. 5 is a flowchart illustrating reverse rotation control execution from the start of a job in an image forming apparatus according to a first embodiment of the present invention. Fig. 6 is a control block diagram illustrating the execution of the control flow. The control flow is calculated and determined by control unit 200 provided in image forming apparatus 100. The flowchart will be described in detail below using an example.

[0051] For example, in the image forming apparatus of this embodiment, when the control unit 200 receives a print start signal (S101), it adds the cumulative number of sheets (number of images formed) since the previous reverse rotation control was executed to a memory unit N (S102). In this embodiment, the initial value of N is set to 0.

[0052] If the job number N exceeds the specified reverse rotation number (Yes in S103), the control unit 200 performs the next reverse rotation operation during the post-rotation period after the final page of the job is printed. That is, the control unit 200 controls the drive source 300, which serves as the drive means for the intermediate transfer belt, to rotate the intermediate transfer belt 7 in the reverse direction (S104). At this time, the amount of reverse rotation of the intermediate transfer belt 7 is set to be longer than the belt circumferential distance L between the cleaning scraper 86 and the blade. Then, the control unit 200 ends the copy / print operation in S105. On the other hand, if the job number N does not exceed the specified reverse rotation number (No in S103), the control unit 200 ends the copy / print operation in S105 without performing the reverse rotation operation.

[0053] 5 in this embodiment are pre- and post-preparation operations before and after the print job is executed. The preparatory operations include starting and stopping the drive of the photosensitive member 1, the developing device 4, and the intermediate transfer belt 7, and starting and stopping the application of high voltage to the charging roller 2, the developing roller 41, the primary transfer roller 5, and the secondary transfer roller 9. Here, the details of the control sequence of the pre- and post-rotation are omitted.

[0054] Furthermore, in this embodiment, the reverse rotation operation is set to a post-rotation operation when the job number N is 1000 sheets or more, but this is not limitative, and the reverse rotation operation may be performed every post-rotation or between sheets.

[0055] Furthermore, in addition to the reverse rotation operation of this embodiment, the following reverse rotation operation (second reverse rotation operation) may be performed. That is, the intermediate transfer belt 7 may be rotated in reverse under predetermined conditions (each post-rotation / cumulative number of sheets, etc.) for the purpose of removing paper dust and the like stuck in the cleaning blade or to alleviate deformation of the cleaning blade. The predetermined conditions for performing the second reverse rotation operation may be different from the conditions for performing the first reverse rotation operation. The amount of operation of this reverse rotation operation may be smaller than that of the reverse rotation operation described above.

[0056] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-described embodiments. [Explanation of symbols]

[0057] 1 photoreceptor 2 Charging roller 3 Exposure equipment 5 Primary transfer roller 7 Intermediate transfer belt 8 Belt cleaning device 82 Cleaning blade 86 Cleaning Scraper

Claims

1. an image carrier that is rotatably provided and that carries a toner image; a transfer member that transfers the toner image formed on the image carrier onto a recording material; a cleaning blade provided in contact with the image carrier at a first contact portion, the cleaning blade cleaning the toner remaining on the image carrier; a scraper that contacts the image carrier at a second contact portion that is downstream of the first contact portion in a rotation direction of the image carrier; a drive source that drives the image carrier; a control unit that controls the drive source to perform a reverse rotation operation of rotating the image carrier in the reverse direction, The image forming apparatus is characterized in that, when performing the reverse rotation operation, the control unit controls the drive source so that the movement distance of the image carrier when it rotates in reverse is longer than the circumferential distance L of the image carrier between the first contact portion and the second contact portion.

2. The image forming apparatus according to claim 1 , wherein the control unit executes the reverse rotation operation based on the number of sheets on which images are formed.

3. 2. The image forming apparatus according to claim 1, wherein the reverse rotation operation is a first reverse rotation operation, and the control unit executes the first reverse rotation operation under a first condition, and executes the second reverse rotation operation under a second condition different from the first condition.

4. 4. The image forming apparatus according to claim 3, wherein in the second reverse rotation operation, a moving distance when the image carrier is rotated in the reverse direction is shorter than the circumferential distance.

Images