JP2015087410A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing the degradation of image quality caused by the contamination of the surface of a transfer roller with toner.SOLUTION: The image forming apparatus includes an intermediate transfer belt 421 to which a toner image formed on a photoreceptor drum 413 is transferred, a primary transfer roller 422 brought into press-contact with the photoreceptor drum 413 across the intermediate transfer belt 421, a press-contact condition changing part changing the press-contact condition of the primary transfer roller 422 with respect to the photoreceptor drum 413, a cleaning blade 95 provided on the downstream side of the primary transfer roller 422 in the traveling direction of the intermediate transfer belt 421 and on the inner peripheral surface side of the intermediate transfer belt 421 and removing the toner transferred to the inner peripheral surface of the intermediate transfer belt 421 from the surface of the primary transfer roller 422, and a control part 100 controlling the press-contact condition changing part, so that the press-contact condition is changed so as to make the amount of the toner transferred to the inner peripheral surface of the intermediate transfer belt 421 from the surface of the primary transfer roller 422 higher than usual.

Description

  The present invention relates to an image forming apparatus.

  In general, an image forming apparatus (printer, copier, facsimile, etc.) using an electrophotographic process technology generates an electrostatic latent image by irradiating (exposing) a charged photoconductor with a laser beam based on image data. Form. Then, by supplying toner from the developing device to the photosensitive member (image carrier) on which the electrostatic latent image is formed, the electrostatic latent image is visualized to form a toner image. Further, after the toner image is directly or indirectly transferred to the paper, it is fixed by heating and pressurizing to form an image on the paper.

  Incidentally, the toner used for the image forming process is stored in a toner hopper (storage unit), a developing device, a cleaning device, a waste toner storage unit, and the like. It may leak from the joint. In this case, the leaked toner may be scattered by the airflow in the apparatus, and the entire apparatus may become dirty. In particular, in an intermediate transfer belt type image forming apparatus, scattered toner may enter the inner peripheral surface side of the intermediate transfer belt and adhere to the surface of a primary transfer roller disposed on the inner peripheral surface side. . As described above, when the surface of the primary transfer roller is contaminated with toner, the resistance of the primary transfer roller increases, so that the transfer bias to the primary transfer roller is not effectively applied. As a result, there arises a problem that the transfer efficiency is lowered and the image quality is lowered.

  In order to solve the above problem, a reverse bias is applied to the primary transfer unit to transfer the toner to the intermediate transfer belt, and then the toner transferred to the surface of the intermediate transfer belt is disposed inside the intermediate transfer belt. In addition, a technique for removing with an intermediate transfer belt back surface cleaner has been proposed (see, for example, Patent Document 1).

JP 2008-170815 A

  However, since the toner that scatters and adheres to the surface of the primary transfer roller is weakly charged, simply apply a reverse bias to the primary transfer roller as in the technique described in Patent Document 1 above. Then, it is difficult to sufficiently transfer the toner to the intermediate transfer belt. That is, the technique described in Patent Document 1 does not provide a sufficient solution to the problem that the image quality deteriorates due to the surface of the primary transfer roller being soiled with toner.

  An object of the present invention is to provide an image forming apparatus capable of preventing a decrease in image quality due to the surface of a transfer roller being soiled with toner.

An image forming apparatus according to the present invention includes:
A photoreceptor on which a toner image is formed;
An intermediate transfer member to which a toner image formed on the photosensitive member is transferred;
A transfer roller pressed against the photoconductor across the intermediate transfer body;
A pressure contact condition changing unit that changes a pressure contact condition of the transfer roller with respect to the photoconductor;
Cleaning that is provided on the downstream side of the transfer roller in the running direction of the intermediate transfer member and on the inner peripheral surface side of the intermediate transfer member, and removes toner transferred from the surface of the transfer roller to the inner peripheral surface of the intermediate transfer member. And
A control unit that controls the pressure contact condition changing unit, and changes the pressure contact condition so that the amount of toner transferred from the surface of the transfer roller to the inner peripheral surface of the intermediate transfer member is increased than normal.
It is characterized by providing.

  According to the present invention, the pressure contact condition of the transfer roller with respect to the photoconductor is changed, and the transfer amount of the toner adhering to the surface of the transfer roller to the inner peripheral surface of the intermediate transfer body is increased from the normal time. The toner on the surface of the roller is sufficiently removed. Accordingly, it is possible to prevent the resistance of the transfer roller from increasing due to the surface of the transfer roller being contaminated with toner, and thus to prevent the image quality from being deteriorated.

1 is a diagram schematically showing an overall configuration of an image forming apparatus in the present embodiment. 2 is a diagram illustrating a main part of a control system of the image forming apparatus in the present embodiment. FIG. It is a figure which shows the structure which changes pressure-contact conditions in this Embodiment. 4 is a flowchart illustrating a pressure contact condition changing operation of the image forming apparatus in the present embodiment. 6 is a table showing the relationship between the amount of toner adhering to the surface of the primary transfer roller, image forming conditions, and usage history of the primary transfer roller. It is a table | surface showing the pressure contact conditions of the primary transfer roller with respect to a photoreceptor drum.

Hereinafter, the present embodiment will be described in detail with reference to the drawings.
[Configuration of Image Forming Apparatus 1]
FIG. 1 is a diagram schematically showing an overall configuration of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 2 shows a main part of the control system of the image forming apparatus 1 according to the present embodiment. An image forming apparatus 1 shown in FIGS. 1 and 2 is an intermediate transfer type color image forming apparatus using electrophotographic process technology. That is, the image forming apparatus 1 transfers the toner images of Y (yellow), M (magenta), C (cyan), and K (black) formed on the photosensitive drum 413 to the intermediate transfer belt 421 (primary transfer). Then, after superposing four color toner images on the intermediate transfer belt 421, the toner images are transferred to the paper S (secondary transfer) to form an image.

  Further, in the image forming apparatus 1, the photosensitive drums 413 corresponding to the four colors of YMCK are arranged in series in the running direction of the intermediate transfer belt 421, and the respective color toner images are sequentially transferred to the intermediate transfer belt 421 in one step. Tandem system is adopted.

  As shown in FIG. 2, the image forming apparatus 1 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a paper transport unit 50, a fixing unit 60, a transfer roller driving unit 75, and voltage application. Unit 80, first cam drive unit 85, second cam drive unit 90, and control unit 100.

  The control unit 100 includes a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, and the like. The CPU 101 reads a program corresponding to the processing content from the ROM 102 and develops it in the RAM 103, and centrally controls the operation of each block of the image forming apparatus 1 in cooperation with the developed program. At this time, various data stored in the storage unit 72 is referred to. The storage unit 72 includes, for example, a nonvolatile semiconductor memory (so-called flash memory) or a hard disk drive.

  The control unit 100 transmits and receives various data to and from an external device (for example, a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 71. Do. For example, the control unit 100 receives image data transmitted from an external device, and forms an image on the paper S based on the image data (input image data). The communication unit 71 is composed of a communication control card such as a LAN card, for example.

  The image reading unit 10 includes an automatic document feeder 11 called an ADF (Auto Document Feeder), a document image scanning device 12 (scanner), and the like.

  The automatic document feeder 11 transports the document D placed on the document tray by a transport mechanism and sends it out to the document image scanning device 12. The automatic document feeder 11 can continuously read images (including both sides) of a large number of documents D placed on the document tray all at once.

  The document image scanning device 12 optically scans a document conveyed on the contact glass from the automatic document feeder 11 or a document placed on the contact glass, and reflects light from the document to a CCD (Charge Coupled Device). ) An image is formed on the light receiving surface of the sensor 12a, and an original image is read. The image reading unit 10 generates input image data based on the reading result by the document image scanning device 12. The input image data is subjected to predetermined image processing in the image processing unit 30.

  The operation display unit 20 is configured by, for example, a liquid crystal display (LCD) with a touch panel, and functions as a display unit 21 and an operation unit 22. The display unit 21 displays various operation screens, image states, operation states of functions, and the like according to a display control signal input from the control unit 100. The operation unit 22 includes various operation keys such as a numeric keypad and a start key, receives various input operations by the user, and outputs an operation signal to the control unit 100.

  The image processing unit 30 includes a circuit that performs digital image processing on input image data according to initial settings or user settings. For example, the image processing unit 30 performs gradation correction based on the gradation correction data (gradation correction table) under the control of the control unit 100. Further, the image processing unit 30 performs various correction processes such as color correction and shading correction, a compression process, and the like on the input image data in addition to the gradation correction. The image forming unit 40 is controlled based on the image data subjected to these processes.

  The image forming unit 40 is based on the input image data, and image forming units 41Y, 41M, 41C, 41K, and an intermediate transfer unit 42 for forming an image using colored toners of Y component, M component, C component, and K component. Etc.

  The Y component, M component, C component, and K component image forming units 41Y, 41M, 41C, and 41K have the same configuration. For convenience of illustration and explanation, common constituent elements are denoted by the same reference numerals, and Y, M, C, or K are added to the reference numerals when distinguished from each other. In FIG. 1, only the components of the Y-component image forming unit 41Y are denoted by reference numerals, and the constituent elements of the other image forming units 41M, 41C, and 41K are omitted.

  The image forming unit 41 includes an exposure device 411, a developing device 412, a photosensitive drum 413 (photosensitive member), a charging device 414, a drum cleaning device 415, and the like.

  The photosensitive drum 413 has an undercoat layer (UCL) and a charge generation layer (CGL) on the peripheral surface of an aluminum conductive cylinder (aluminum tube) having a drum diameter of 80 mm, for example. It is a negatively charged organic photoconductor (OPC) in which a generation layer (CTL) and a charge transport layer (CTL) are sequentially stacked. The charge generation layer is made of an organic semiconductor in which a charge generation material (for example, phthalocyanine pigment) is dispersed in a resin binder (for example, polycarbonate), and generates a pair of positive charges and negative charges by exposure by the exposure device 411. The charge transport layer consists of a material in which a hole transport material (electron donating nitrogen-containing compound) is dispersed in a resin binder (for example, polycarbonate resin), and transports positive charges generated in the charge generation layer to the surface of the charge transport layer. To do.

  The control unit 100 controls a drive current supplied to a drive motor (not shown) that rotates the photosensitive drum 413, so that the photosensitive drum 413 rotates at a constant peripheral speed.

  The charging device 414 uniformly charges the surface of the photoconductive drum 413 to a negative polarity. The exposure device 411 is composed of, for example, a semiconductor laser, and irradiates the photosensitive drum 413 with laser light corresponding to the image of each color component. A positive charge is generated in the charge generation layer of the photosensitive drum 413 and is transported to the surface of the charge transport layer, whereby the surface charge (negative charge) of the photosensitive drum 413 is neutralized. An electrostatic latent image of each color component is formed on the surface of the photosensitive drum 413 due to a potential difference from the surroundings.

  The developing device 412 is a two-component developing type developing device, and attaches toner of each color component to the surface of the photosensitive drum 413 to visualize the electrostatic latent image to form a toner image.

  The drum cleaning device 415 includes a drum cleaning blade that is slidably contacted with the surface of the photosensitive drum 413, and removes transfer residual toner remaining on the surface of the photosensitive drum 413 after primary transfer. The drum unit including the photosensitive drum 413 is provided with a lubricant application device that applies the lubricant, which has been scraped off by the lubricant application brush, into powder, on the photosensitive drum 413.

  The intermediate transfer unit 42 includes an intermediate transfer belt 421 (intermediate transfer member), a primary transfer roller 422 (transfer roller), a plurality of support rollers 423, a secondary transfer roller 424, a belt cleaning device 426, and the like.

  The intermediate transfer belt 421 is an endless belt, and is stretched around a plurality of support rollers 423 in a loop shape. At least one of the plurality of support rollers 423 is configured by a driving roller, and the other is configured by a driven roller. For example, it is preferable that the roller 423A disposed downstream of the K component primary transfer roller 422 in the belt traveling direction is a drive roller. This makes it easy to keep the belt running speed constant in the primary transfer portion. As the driving roller 423A rotates, the intermediate transfer belt 421 travels in the direction of arrow A at a constant speed.

  The intermediate transfer belt 421 is a belt having conductivity and elasticity, and has a high resistance layer having a volume resistivity of 8 to 11 [log Ω · cm] on the surface. The intermediate transfer belt 421 is rotationally driven by a control signal from the control unit 100. Note that the material, thickness, and hardness of the intermediate transfer belt 421 are not limited as long as they have conductivity and elasticity.

  The primary transfer roller 422 is a foaming roller having a cored bar and an elastic layer covering the outer periphery of the cored bar. The material of the metal core is a metal such as aluminum. The material of the elastic layer is a polyurethane foam having conductivity. The primary transfer roller 422 is disposed on the inner peripheral surface side of the intermediate transfer belt 421 so as to face the photosensitive drum 413 of each color component. The primary transfer roller 422 is pressed against the photosensitive drum 413 with the intermediate transfer belt 421 interposed therebetween, thereby forming a primary transfer nip for transferring a toner image from the photosensitive drum 413 to the intermediate transfer belt 421.

  The secondary transfer roller 424 is disposed on the outer peripheral surface side of the intermediate transfer belt 421 so as to face a roller 423B (hereinafter referred to as “backup roller 423B”) disposed on the downstream side of the driving roller 423A in the belt traveling direction. The secondary transfer roller 424 is pressed against the backup roller 423B with the intermediate transfer belt 421 interposed therebetween, thereby forming a secondary transfer nip for transferring the toner image from the intermediate transfer belt 421 to the paper S.

  When the intermediate transfer belt 421 passes through the primary transfer nip, the toner images on the photoconductive drum 413 are primarily transferred onto the intermediate transfer belt 421 in sequence. Specifically, a primary transfer bias is applied to the primary transfer roller 422, and an electric charge having a polarity opposite to that of the toner is applied to the back side of the intermediate transfer belt 421 (the side in contact with the primary transfer roller 422). It is electrostatically transferred to the intermediate transfer belt 421.

  Thereafter, when the sheet S passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred to the sheet S. Specifically, a toner image is applied by applying a secondary transfer bias to the secondary transfer roller 424 and applying a charge having a polarity opposite to that of the toner to the back side of the paper S (the side in contact with the secondary transfer roller 424). Is electrostatically transferred to the paper S. The sheet S to which the toner image is transferred is conveyed toward the fixing unit 60.

  The belt cleaning device 426 removes transfer residual toner remaining on the surface of the intermediate transfer belt 421 after the secondary transfer. Instead of the secondary transfer roller 424, a configuration (so-called belt-type secondary transfer unit) in which a secondary transfer belt is looped around a plurality of support rollers including the secondary transfer roller is adopted. Also good.

  The fixing unit 60 includes an upper fixing unit 60A having a fixing surface side member disposed on the fixing surface (surface on which the toner image is formed) of the paper S, and the back surface (surface opposite to the fixing surface) of the paper S. A lower fixing unit 60B having a rear side support member to be disposed, a heating source 60C, and the like are provided. When the back surface side support member is pressed against the fixing surface side member, a fixing nip for nipping and transporting the paper S is formed.

  The fixing unit 60 fixes the toner image on the paper S by heating and pressurizing the paper S on which the toner image is secondarily transferred and conveyed at the fixing nip. The fixing unit 60 is disposed in the fixing device F as a unit. The fixing device F may be provided with an air separation unit that separates the sheet S from the fixing surface side member or the back surface side support member by blowing air.

  The paper transport unit 50 includes a paper feed unit 51, a paper discharge unit 52, a transport path unit 53, and the like. In the three paper feed tray units 51a to 51c constituting the paper feed unit 51, paper S (standard paper, special paper) identified based on basis weight, size, or the like is stored for each preset type. . The conveyance path unit 53 includes a plurality of conveyance roller pairs such as registration roller pairs 53a.

  The sheets S stored in the sheet feed tray units 51 a to 51 c are sent one by one from the top and are conveyed to the image forming unit 40 by the conveyance path unit 53. At this time, the registration roller portion provided with the registration roller pair 53a corrects the inclination of the fed paper S and adjusts the conveyance timing. In the image forming unit 40, the toner image on the intermediate transfer belt 421 is secondarily transferred onto one side of the sheet S at a time, and a fixing process is performed in the fixing unit 60. The sheet S on which the image has been formed is discharged out of the apparatus by a discharge unit 52 having a discharge roller 52a.

  Next, a configuration around the primary transfer roller 422 for the K component and the photosensitive drum 413 will be described with reference to FIG. The primary transfer roller 422 is disposed on the inner peripheral surface side of the intermediate transfer belt 421 so as to face the photosensitive drum 413. The primary transfer roller 422 is pressed against the photosensitive drum 413 with the intermediate transfer belt 421 interposed therebetween. As shown in FIG. 3, a line L <b> 1 passing through the rotation axis center of the primary transfer roller 422 and the rotation axis center of the photosensitive drum 413 is perpendicular to the intermediate transfer belt 421.

  The primary transfer roller 422 is rotated at a predetermined rotational speed (for example, 460 [mm / mm] by the transfer roller driving unit 75 under the control of the control unit 100 during the image forming process of the image forming apparatus 1 (when executing the print job). s]) to rotate clockwise in the figure. That is, the primary transfer roller 422 rotates in the width direction (direction in which the surfaces facing each other move in the same direction) with respect to the traveling direction (arrow A direction) of the intermediate transfer belt 421.

  The primary transfer roller 422 is connected to the first cam driving unit 85 via a pressing spring 87 and a cam 86. When receiving a drive command from the control unit 100, the first cam drive unit 85 rotates the cam 86 about the shaft 86a. The pressing spring 87 biases the primary transfer roller 422 in the arrow X direction. The primary transfer roller 422 presses the photosensitive drum 413 in the arrow X direction by the biasing force of the pressing spring 87. Depending on the rotational position of the cam 86, the urging force (pressing force) of the primary transfer roller 422 against the photosensitive drum 413 changes. An angle θx formed by a line L1 passing through the rotation axis center of the primary transfer roller 422 and the rotation axis center of the photosensitive drum 413 and the arrow direction X is a predetermined angle (for example, 15 [°]). Hereinafter, the arrow direction X is referred to as a downstream direction X.

  The primary transfer roller 422 is connected to the second cam driving unit 90 via a pressing spring 92 and a cam 91. When the second cam drive unit 90 receives a drive command from the control unit 100, the second cam drive unit 90 rotates the cam 91 about the shaft 91a. The pressing spring 92 biases the primary transfer roller 422 in the arrow Y direction. The primary transfer roller 422 presses the photosensitive drum 413 in the arrow Y direction by the biasing force of the pressing spring 92. Depending on the rotational position of the cam 91, the urging force (pressing force) of the primary transfer roller 422 against the photosensitive drum 413 changes. An angle θy formed by a line L1 passing through the rotation axis center of the primary transfer roller 422 and the rotation axis center of the photosensitive drum 413 and the arrow direction Y is a predetermined angle (for example, 7 [°]). Hereinafter, the arrow direction Y is referred to as the upstream direction Y.

  The control unit 100 performs the first cam driving unit 85 and the second cam driving unit 90 so that the pressing direction of the primary transfer roller 422 against the photosensitive drum 413 becomes the downstream direction X during the image forming process of the image forming apparatus 1. To control.

  A voltage application unit 80 is connected to the primary transfer roller 422 as a power source for applying a predetermined bias (voltage) to the primary transfer roller 422. In the image forming process of the image forming apparatus 1, the voltage application unit 80 receives a control signal from the control unit 100 and transfers the toner image formed on the photosensitive drum 413 to the intermediate transfer belt 421. A primary transfer bias (transfer voltage) of an image charging polarity (minus polarity) and a reverse polarity (plus polarity) is applied to the primary transfer roller 422.

  A cleaning blade 95 (cleaning unit) is provided on the downstream side of the primary transfer roller 422 in the traveling direction of the intermediate transfer belt 421 and on the inner peripheral surface side of the intermediate transfer belt 421 so as to contact the surface of the intermediate transfer belt 421. Yes. The cleaning blade 95 has the tip (blade edge) of the cleaning blade 95 in contact with the surface of the intermediate transfer belt 421 at a counter with respect to the traveling direction of the intermediate transfer belt 421. The material of the cleaning blade 95 is, for example, urethane rubber (hardness: 74 [degrees], rebound resilience: 23 [%]), but any other elastic material may be used.

  The cleaning blade 95 is attached to a support metal plate (not shown) that supports the cleaning blade 95. The cleaning blade 95 scrapes and removes toner transferred from the surface of the primary transfer roller 422 to the inner peripheral surface of the intermediate transfer belt 421. The removed toner is collected by a toner collection unit (not shown). As the cleaning unit, in addition to the cleaning blade 95, a cleaning brush or a scraper can be used.

  The transfer roller driving unit 75, the first cam driving unit 85, and the second cam driving unit 90 function as a pressure contact condition changing unit of the present invention.

  Next, the pressure contact condition changing operation of the image forming apparatus 1 will be described with reference to FIG. The pressure contact condition changing operation is an operation for changing the pressure contact condition of the primary transfer roller 422 against the photosensitive drum 413 in order to sufficiently transfer the toner attached to the surface of the primary transfer roller 422 to the inner peripheral surface of the intermediate transfer belt 421. is there. FIG. 4 is a flowchart illustrating an example of the pressure contact condition changing operation of the image forming apparatus 1.

  First, the control unit 100 determines whether or not it is the pressure contact condition change timing (step S100). In the present embodiment, the control unit 100 determines that it is the pressing condition change timing when it is in the warm-up state, and determines that it is not the pressing condition change timing when it is not in the warm-up state. As a result of this determination, when it is not the pressure contact condition change timing (step S100, NO), the processing returns to before step S100.

  On the other hand, when it is the pressure contact condition change timing (step S100, YES), the control unit 100 changes the pressure contact condition of the primary transfer roller 422 to the photosensitive drum 413 (step S120). Specifically, the control unit 100 controls the second cam driving unit 90 so that the pressing direction of the primary transfer roller 422 against the photosensitive drum 413 becomes the upstream direction Y. At this time, the pressing force (for example, 30 [N]) of the primary transfer roller 422 against the photosensitive drum 413 is larger than the pressing force (for example, 26 [N]) when the pressing direction is the downstream direction X. When the pressing direction of the primary transfer roller 422 is the downstream direction X, a discharge occurs between the primary transfer roller 422 and the intermediate transfer belt 421, and the toner on the primary transfer roller 422 is weakly charged. Therefore, in this embodiment, the pressing direction of the primary transfer roller 422 is changed to the upstream direction Y, and a front winding portion of the intermediate transfer belt 421 is formed on the primary transfer roller 422 side. The occurrence of electric discharge with the intermediate transfer belt 421 is suppressed, and the toner on the primary transfer roller 422 is prevented from being weakly charged. Therefore, the amount of electrostatic transfer to the inner peripheral surface of the intermediate transfer belt 421 with respect to the toner adhering to the surface of the primary transfer roller 422 can be increased by applying a transfer voltage in step S140 described later.

  In addition, the control unit 100 rotates the primary transfer roller 422 in a counter direction (a direction in which surfaces facing each other move in the opposite direction, counterclockwise in FIG. 3) with respect to the traveling direction of the intermediate transfer belt 421. Thus, the transfer roller driving unit 75 is controlled. At this time, the rotation speed (for example, 50 [mm / s]) of the primary transfer roller 422 is slower than the rotation speed (for example, 460 [mm / s]) when the pressing direction is the downstream direction X.

  Next, the control unit 100 electrostatically transfers the toner (charge polarity: minus polarity) attached to the surface of the primary transfer roller 422 to the inner peripheral surface of the intermediate transfer belt 421. The voltage application unit 80 is controlled to apply a bias (transition voltage) of the same polarity (negative polarity) to the primary transfer roller 422 (step S140). By the processing in steps S120 and S140, the toner adhering to the surface of the primary transfer roller 422 is sufficiently transferred to the inner peripheral surface of the intermediate transfer belt 421. The toner transferred to the inner peripheral surface of the intermediate transfer belt 421 is scraped off by the cleaning blade 95 and removed.

  Next, the control unit 100 determines whether or not a predetermined time (for example, 30 [s]) has elapsed since the application of the transition voltage to the primary transfer roller 422 (step S160). As a result of this determination, if the predetermined time has not elapsed (step S160, NO), the process returns to before step S160.

  On the other hand, when the predetermined time has elapsed (step S160, YES), the control unit 100 controls the voltage application unit 80 to stop the application of the transfer voltage to the primary transfer roller 422 (step S180). Finally, the control unit 100 restores the pressure contact condition of the primary transfer roller 422 to the photosensitive drum 413 (Step S200). Specifically, the control unit 100 controls the first cam driving unit 85 so that the pressing direction of the primary transfer roller 422 against the photosensitive drum 413 becomes the downstream direction X. Further, the control unit 100 controls the transfer roller driving unit 75 so that the primary transfer roller 422 rotates in the width direction (clockwise direction in FIG. 3) with respect to the traveling direction of the intermediate transfer belt 421. Thereafter, the image forming apparatus 1 ends the processing in FIG.

  In the flowchart shown in FIG. 4, it is preferable that the control unit 100 change the pressure contact condition according to the image forming condition and the usage history of the primary transfer roller 422. Further, the control unit 100 preferably changes the magnitude of the transfer voltage applied to the primary transfer roller 422 according to the image forming conditions and the usage history of the primary transfer roller 422. Further, it is preferable that the control unit 100 controls the timing for changing the pressure contact condition according to the image forming conditions and the usage history of the primary transfer roller 422. Here, the image forming conditions are, for example, the temperature and humidity environment in the image forming apparatus 1, the charge amount of toner used for the image forming process, the image forming mode in the image forming process, and the coverage (printing rate) in the image forming process. The usage history of the primary transfer roller 422 is obtained from, for example, the number of printed sheets in the image forming process.

  FIG. 5 is a table showing the relationship between the amount of toner adhering to the surface of the primary transfer roller 422 (hereinafter referred to as adhering toner amount), the image forming conditions, and the usage history of the primary transfer roller 422. As shown in FIG. 5, in the temperature and humidity environment in the image forming apparatus 1, the amount of adhered toner increases in the order of HH environment, NN environment, and LL environment. This is because, in the HH environment, the charge amount of the toner used for the image forming process is low, and the toner is easily scattered by the airflow in the image forming apparatus 1. For the same reason, the toner used in the image forming process is less than 30 [μC / g], 30 [μC / g] or more and less than 40 [μC / g], and the adhering toner in the order of 40 [μC / g] or more. The amount increases.

  In the image forming mode, the amount of adhered toner increases in the order of the color mode and the monochrome mode. This is because, in the color mode, the amount of toner used for image forming processing increases. In the coverage, the amount of adhered toner increases in the order of 20 [%] or more, 5 [%] or more and less than 20 [%], and less than 5 [%]. This is because when the coverage is 20% or more, the amount of toner used in the image forming process increases. Further, in the usage history (number of printed sheets) of the primary transfer roller 422, the amount of adhered toner increases in the order of less than 50000 [sheets], 50000 [sheets] or more and less than 300000 [sheets], and 300000 [sheets] or more. This is because when the number of printed sheets is less than 50000 [sheets], the cells of the primary transfer roller 422 (foaming roller) are not crushed and the toner easily adheres to the surface of the primary transfer roller 422.

  As described with reference to FIG. 5, the amount of adhered toner changes according to the image forming conditions and the usage history of the primary transfer roller 422, so it is preferable to change the pressure contact condition according to the amount of adhered toner. FIG. 6 is a table showing the pressure contact condition of the primary transfer roller 422 against the photosensitive drum 413. In FIG. 6, change patterns 1, 2, 3, 4 when the pressure contact conditions (pressing force, pressing direction, rotation direction, rotation speed of the primary transfer roller 422) are changed, and when the pressure contact conditions are not changed (during image formation processing) ) Shows a normal pattern. Here, the item “change target of pressure contact condition” indicates which of the primary transfer rollers 422 for the Y component, M component, C component, and K component is to be changed. Yes. The item “current” indicates a current value that flows between the primary transfer roller 422 and the intermediate transfer belt 421 when the voltage application unit 80 applies a transfer voltage or a transfer voltage to the primary transfer roller 422. The item “change timing” indicates the timing of changing the pressure contact condition.

  The change pattern 1 is a pressure contact condition used in the processing in the flowchart shown in FIG. 4, and is a pattern for changing the pressure contact condition for all of the primary transfer rollers 422 for the Y component, M component, C component, and K component. This change pattern 1 is suitable when the amount of adhered toner is small. The change pattern 2 is a pattern for changing the pressure contact condition for all of the primary transfer rollers 422 for the Y component, the M component, the C component, and the K component. Compared with the change pattern 1, the pressing pattern and the pressing direction of the primary transfer roller 422 are changed. In addition to the angle and the rotation speed, the magnitude of the transition voltage (as a result, the absolute value of the current) applied to the primary transfer roller 422 is increased. In the change pattern 2, the pressure contact condition is changed more frequently than in the change pattern 1. As a result, compared with the change pattern 1, the toner attached to the surface of the primary transfer roller 422 can be transferred by the inner peripheral surface of the intermediate transfer belt 421. That is, the change pattern 2 is suitable when the amount of attached toner is large.

  The change pattern 3 is a pattern for changing the pressure contact condition only for the primary transfer roller 422 for the K component. Although the change timing is different, the pressure contact condition is the same as the change pattern 1. The change pattern 3 is suitable when the image forming mode is the monochrome mode, that is, when the amount of adhered toner on the primary transfer roller 422 for the K component increases.

  The change pattern 4 is a pattern for changing the pressure contact conditions for all of the primary transfer rollers 422 for the Y component, M component, C component, and K component. Although the pressing force and the pressing direction are different, the other pressure contact conditions are normal. Same as pattern. The change pattern 4 adheres to the surface of the primary transfer roller 422 during the image forming process of the image forming apparatus 1 when toner dropout and toner scattering are difficult to occur (for example, when the temperature and humidity environment is an NN environment). This is suitable when the toner is to be transferred to the inner peripheral surface of the intermediate transfer belt 421 even mechanically. This is because the toner dropout is likely to occur by increasing the pressing force of the primary transfer roller 422 when the temperature and humidity environment is the LL environment. When the temperature and humidity environment is an HH environment, the toner scattering occurs when the pressing direction of the primary transfer roller 422 is changed to the upstream direction Y to cause discharge between the photosensitive drum 413 and the intermediate transfer belt 421. It is easy to do.

[Effects of the present embodiment]
As described above in detail, in the present embodiment, the image forming apparatus 1 includes the photosensitive drum 413 on which the toner image is formed, and the intermediate transfer belt 421 on which the toner image formed on the photosensitive drum 413 is transferred. A primary transfer roller 422 that is pressed against the photosensitive drum 413 across the intermediate transfer belt 421, a pressure contact condition changing unit that changes a pressure contact condition of the primary transfer roller 422 against the photosensitive drum 413, and a traveling direction of the intermediate transfer belt 421. And a cleaning blade 95 that is provided on the downstream side of the primary transfer roller 422 and on the inner peripheral surface side of the intermediate transfer belt 421, and removes the toner transferred from the surface of the primary transfer roller 422 to the inner peripheral surface of the intermediate transfer belt 421. Control the condition changer to transfer from the surface of the primary transfer roller 422 to the inner peripheral surface of the intermediate transfer belt 421 That the amount of toner and a control unit 100 to change the pressure conditions so as to increase from the normal.

  According to the present embodiment configured as described above, the pressure contact condition of the primary transfer roller 422 with respect to the photosensitive drum 413 is changed, and the inner peripheral surface of the intermediate transfer belt 421 with respect to the toner adhering to the surface of the primary transfer roller 422. Therefore, the toner on the surface of the primary transfer roller 422 is sufficiently removed. Accordingly, it is possible to prevent the resistance of the primary transfer roller 422 from increasing due to the surface of the primary transfer roller 422 being contaminated with toner, and thus to prevent the image quality from being deteriorated. Further, the durability of the primary transfer roller 422 can be improved by removing the toner on the surface of the primary transfer roller 422. Further, by transferring the toner on the surface of the primary transfer roller 422 to the intermediate transfer belt 421 and cleaning the surface of the primary transfer roller 422, the surface of the primary transfer roller 422 is directly cleaned with a scraper or the like. It is possible to prevent the surface from being scratched.

  In this embodiment, the cleaning blade 95 is provided on the downstream side of the primary transfer roller 422 disposed on the most downstream side in the traveling direction of the intermediate transfer belt 421. Thereby, it is possible to prevent the toner transferred to the inner peripheral surface of the intermediate transfer belt 421 from transferring to another member (for example, a tension roller or a driving roller) in contact with the intermediate transfer belt 421.

  In the above embodiment, the example in which the pressing condition is the pressing direction of the primary transfer roller 422, the pressing force of the primary transfer roller 422, the rotation direction of the primary transfer roller 422, and the rotation speed of the primary transfer roller 422 has been described. However, the present invention is not limited to this. That is, the pressing condition may be at least one of the pressing direction of the primary transfer roller 422, the pressing force of the primary transfer roller 422, the rotation direction of the primary transfer roller 422, and the rotation speed of the primary transfer roller 422.

  In the above embodiment, an example in which the primary transfer roller 422 is a foaming roller has been described, but the present invention is not limited to this.

  In the above embodiment, the cleaning blade 95 may be provided on the downstream side of each primary transfer roller 422 in the traveling direction of the intermediate transfer belt 421. This prevents the toner transferred from the upstream primary transfer roller 422 to the inner peripheral surface of the intermediate transfer belt 421 in the traveling direction of the intermediate transfer belt 421 from reattaching to the downstream primary transfer roller 422. it can.

  In the above-described embodiment, the pressure contact condition may be changed for any primary transfer roller 422 among the primary transfer rollers 422 for the Y component, M component, C component, and K component.

  In addition, each of the above-described embodiments is merely an example of actualization in carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. That is, the present invention can be implemented in various forms without departing from the gist or the main features thereof.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Image reading part 20 Operation display part 21 Display part 22 Operation part 30 Image processing part 40 Image forming part 50 Paper conveyance part 60 Fixing part 71 Communication part 72 Storage part 75 Transfer roller drive part 80 Voltage application part 85 No. 1 cam drive unit 86, 91 cam 87, 92 pressure spring 90 second cam drive unit 95 cleaning blade 100 control unit 101 CPU
102 ROM
103 RAM
421 Intermediate transfer belt 422 Primary transfer roller

Claims (9)

A photoreceptor on which a toner image is formed;
An intermediate transfer member to which a toner image formed on the photosensitive member is transferred;
A transfer roller pressed against the photoconductor across the intermediate transfer body;
A pressure contact condition changing unit that changes a pressure contact condition of the transfer roller with respect to the photoconductor;
Cleaning that is provided on the downstream side of the transfer roller in the running direction of the intermediate transfer member and on the inner peripheral surface side of the intermediate transfer member, and removes toner transferred from the surface of the transfer roller to the inner peripheral surface of the intermediate transfer member. And
A control unit that controls the pressure contact condition changing unit, and changes the pressure contact condition so that the amount of toner transferred from the surface of the transfer roller to the inner peripheral surface of the intermediate transfer member is increased than normal.
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the control unit changes the pressure contact condition according to an image forming condition. A voltage application unit that applies a transfer voltage having the same polarity as the charging polarity of the toner attached to the surface of the transfer roller to the transfer roller;
The image forming apparatus according to claim 2, wherein the control unit controls the voltage application unit to change the magnitude of the transition voltage according to the image forming condition.   The image forming apparatus according to claim 3, wherein the control unit controls a timing of changing the pressure contact condition according to the image forming condition.   The image forming apparatus according to claim 1, wherein the control unit changes the pressure contact condition according to a use history of the transfer roller. A voltage application unit that applies a transfer voltage having the same polarity as the charging polarity of the toner attached to the surface of the transfer roller to the transfer roller;
The image forming apparatus according to claim 5, wherein the control unit controls the voltage application unit to change the magnitude of the transition voltage according to a use history of the transfer roller.   The image forming apparatus according to claim 6, wherein the control unit controls timing for changing the pressure contact condition according to a use history of the transfer roller.   The image forming apparatus according to claim 1, wherein the transfer roller is a foaming roller.   The pressure contact condition is at least one of a pressing direction of the transfer roller, a pressing force of the transfer roller, a rotation direction of the transfer roller, and a rotation speed of the transfer roller. The image forming apparatus according to claim 1.