JP5409945B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a tandem color image forming apparatus in which a plurality of image forming units including a photoconductor are arranged in parallel along an intermediate transfer belt.

  In an image forming apparatus using an electrophotographic system such as a copying machine, a printer, or a FAX, a powder developer (hereinafter referred to as toner) is mainly used, and an electrostatic image formed on an image carrier such as a photosensitive drum. In general, the latent image is visualized with toner in the developing device, and the toner image is transferred onto a recording medium, and then a fixing process is performed.

  In the image forming apparatus as described above, in addition to the direct transfer method in which the toner image is directly transferred from the photosensitive drum, which is an image carrier, to the recording medium, the toner image is transferred on the intermediate transfer belt and then recorded. There is an intermediate transfer type image forming apparatus that re-transfers onto a medium. The intermediate transfer method is widely used in a tandem color image forming apparatus that forms one image by a plurality of image forming units.

  The intermediate transfer belt used in the intermediate transfer system generally has various configurations such as a single resin layer and an elastic layer provided on the surface of the resin layer, and further provided with a coating layer. Some have a high surface friction coefficient. When the friction coefficient is high, the adhesion force of the toner to the surface of the intermediate transfer belt is increased, and the transfer performance to the recording medium is lowered. Specifically, the center of the line image or character image is missing, so-called hollowing out phenomenon, or the toner adherence is lowered in the concave portion of the recording medium having a large surface irregularity such as rough paper, and the void is generated and transferred. A so-called image blur phenomenon occurs in which the toner is not transferred due to the weakened electric field.

  In addition, since the wrapping property (tackiness) of the recording medium with respect to the photosensitive drum is also improved, in the case of a tandem color image forming apparatus that forms one image by a plurality of image forming units, there is an intermediate between the photosensitive drums of each color. The transfer belt expands and contracts, the position of each color toner image is deteriorated, and color misregistration easily occurs.

  Therefore, a method for reducing the surface friction coefficient of the intermediate transfer belt has been proposed. For example, Patent Document 1 discloses a toner external additive (hereinafter simply referred to as fluidity-imparting additive) for imparting fluidity to at least the entire transferable region of the intermediate transfer member. After transferring the toner containing the external additive), the toner is removed and a part of the external additive is left on the intermediate transfer member, so that the toner releasability on the surface of the intermediate transfer member is almost uniform. An image forming apparatus that is improved to improve transferability is disclosed.

JP 2001-134109 A

  However, in the method of Patent Document 1, since the adhesive force of the external additive remaining on the intermediate transfer member is weak, the residual external additive adheres to the next transferred toner image, and the toner is collected in the cleaning unit. In this case, there is a problem that the external additive is also removed. Patent Document 1 describes that a primary image transfer and removal of a toner image are repeated a plurality of times, so that there is an effect of suppressing a hollow image and a ghost image (paragraphs [0060] to [0065]). However, it is considered that a considerable amount of time is required to completely eliminate the void phenomenon and the image blurring phenomenon.

  SUMMARY OF THE INVENTION In view of the above problems, the present invention provides an image forming apparatus capable of improving the transferability to a recording medium by reducing the friction coefficient of the surface of the intermediate transfer member and effectively suppressing the hollowing out phenomenon and the image blurring phenomenon. The purpose is to do.

  To achieve the above object, according to a first configuration of the present invention, an electrostatic latent image is formed by supplying an image carrier on which an electrostatic latent image is formed and supplying toner containing an external additive to the surface of the image carrier. A plurality of image forming units including a developing device that forms a toner image according to the above, an endless intermediate transfer member on which the toner image formed on the image carrier is primarily transferred in the image forming unit, A toner image formed on the image carrier in a state where a linear velocity difference is provided between the image carrier and the intermediate transfer member during non-image formation. A toner adhesion mode in which toner is adhered to the entire image formable width of the intermediate transfer body by transferring a predetermined number of times onto the body can be executed, and the toner adhesion mode includes a part of the plurality of image carriers. A linear velocity difference was given to the intermediate transfer member. A first adhesion step for transferring the toner image onto the intermediate transfer member in the state, and transferring the toner image formed on the image carrier by the first attachment step over the entire image formable width of the intermediate transfer member. After that, an idling process for continuing driving for a predetermined time in a state where a linear velocity difference is provided between the image carrier and the intermediate transfer body, and after the idling process, the first adhering process is more than the first adhering process. And a second adhesion step of transferring the toner image onto the intermediate transfer body by increasing the image carrier having a linear velocity difference with the intermediate transfer body in a stepwise manner.

  According to the first configuration of the present invention, since the surface of the intermediate transfer member is repeatedly rubbed by the image carrier by performing the idle rotation step after the first attachment step, the external additive is added to the intermediate transfer member. Adhesion is improved. In addition, by executing the second adhesion step after the idling step, a new external additive can be supplied to the intermediate transfer member while the external additive having a low adhesion strength is adhered to the toner and collected. Thereby, the adhesion amount and adhesion strength of the external additive can be increased efficiently, and the occurrence of uneven adhesion of the external additive during the subsequent normal image output can be prevented.

1 is a schematic cross-sectional view showing the overall configuration of an image forming apparatus of the present invention. Partial enlarged view of the periphery of the image forming portion Pa in FIG. Sectional drawing which shows the example of 1 structure of the intermediate transfer belt used for the image forming apparatus of this invention 1 is a block diagram showing a control path of an image forming apparatus of the present invention. The top view which shows the halftone image transferred to the transferable area of the intermediate transfer belt in the toner adhesion mode A plan view showing a state in which an external additive adheres to the transferable area of the intermediate transfer belt A graph showing the relationship between the toner adhesion mode execution time and the glossiness of the intermediate transfer belt surface when the deceleration rate of the photosensitive drum with respect to the intermediate transfer belt is changed stepwise The graph showing the relationship between the toner adhesion mode execution time and the dynamic friction coefficient of the surface of the intermediate transfer belt when the deceleration rate of the photosensitive drum with respect to the intermediate transfer belt is changed stepwise Graph showing the relationship between the glossiness of the intermediate transfer belt surface and the dynamic friction coefficient of the intermediate transfer belt surface A graph showing the relationship between the dynamic friction coefficient of the surface of the intermediate transfer belt and the image roughness 6 is a flowchart illustrating an example of toner adhesion mode control executed in the image forming apparatus according to the first embodiment of the present invention. 9 is a flowchart illustrating an example of toner adhesion mode control executed in the image forming apparatus according to the second exemplary embodiment of the present invention. 10 is a flowchart illustrating a control example of a toner adhesion mode executed in the image forming apparatus according to the third embodiment of the present invention. Belt drive time when only solid image pattern is output after four times aging (belt idling), halftone image pattern is repeatedly output, and halftone image pattern is repeatedly output after 60 seconds of aging Showing the relationship between belt surface gloss and belt surface gloss 10 is a flowchart illustrating a control example of a toner adhesion mode executed in the image forming apparatus according to the fourth exemplary embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of a tandem color image forming apparatus of the present invention. In the main body of the color printer 100, four image forming portions Pa, Pb, Pc, and Pd are arranged in order from the right side in FIG. These image forming portions Pa to Pd are provided corresponding to images of four different colors (magenta, cyan, yellow, and black), and magenta, cyan, and yellow are respectively subjected to charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  The image forming portions Pa to Pd are provided with photosensitive drums 1a, 1b, 1c and 1d each having a photosensitive layer made of amorphous silicon for carrying a visible image (toner image) of each color. The intermediate transfer belt 8 that rotates clockwise is provided adjacent to the image forming portions Pa to Pd. The toner images formed on the photosensitive drums 1a to 1d are sequentially transferred onto the intermediate transfer belt 8 that moves while contacting the photosensitive drums 1a to 1d. Then, the toner image is transferred onto the sheet P in the fixing device 7 and then discharged from the apparatus main body. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG.

  The paper P onto which the toner image is transferred is housed in a paper cassette 16 at the lower part of the apparatus, and is conveyed to the secondary transfer roller 9 via the paper feed roller 12a and the registration roller pair 12b. A sheet made of dielectric resin is used for the intermediate transfer belt 8, and an endless (seamless) belt having no seam is mainly used. The intermediate transfer belt 8 and the secondary transfer roller 9 are rotationally driven by a belt drive motor 45 (see FIG. 4) at substantially the same linear speed as the photosensitive drums 1a to 1d (+ 0.1% as a linear speed ratio with respect to the photosensitive drum). Is done. In addition, a belt cleaning device 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed on the upstream side in the moving direction of the intermediate transfer belt 8 as viewed from the image forming portion Pa.

  Next, the image forming units Pa to Pd will be described. There are chargers 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d that are rotatably arranged. The exposure device 4 for exposing the toner, the developing devices 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the developer (toner) remaining on the photosensitive drums 1a to 1d are removed. Cleaning devices 5a, 5b, 5c and 5d are provided.

  When image data is input from a host device such as a personal computer, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, and then light is irradiated according to the image data by the exposure device 4. The electrostatic latent images corresponding to the image data are formed on the respective photosensitive drums 1a to 1d. Each of the developing devices 3a to 3d includes a developing roller (developer carrying member) disposed opposite to the photosensitive drums 1a to 1d, and toners of each color of yellow, cyan, magenta, and black are supplied by a replenishing device (not shown). A predetermined amount is filled. The toner is supplied onto the photosensitive drums 1a to 1d by the developing rollers of the developing devices 3a to 3d, and electrostatically adheres to the electrostatic latent image formed by exposure from the exposure device 4. A toner image is formed.

  Then, by applying a predetermined transfer voltage to the primary transfer rollers 6a to 6d that are driven to rotate with respect to the intermediate transfer belt 8, magenta, cyan, yellow, and black toner images on the photosensitive drums 1a to 1d are intermediate transferred. Primary transfer is performed on the belt 8. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning devices 5a to 5d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched around a driven roller 10, a drive roller 11, and a tension roller 20, and the intermediate transfer belt 8 rotates clockwise as the drive roller 11 is rotated by a belt drive motor 45 (see FIG. 4). Is started, the sheet P is conveyed from the registration roller 12b to the nip portion (secondary transfer nip portion) between the secondary transfer roller 9 and the intermediate transfer belt 8 provided adjacent to the intermediate transfer belt 8 at a predetermined timing. The full color image is secondarily transferred onto the paper P at the nip portion. The paper P on which the toner image is transferred is conveyed to the fixing device 7.

  The sheet P conveyed to the fixing device 7 is heated and pressurized when passing through the nip portion (fixing nip portion) of the pair of fixing rollers 13 to fix the toner image on the surface of the sheet P, and a predetermined full color image is formed. It is formed. The paper P on which the full-color image is formed is distributed in the transport direction by the branching section 14 that branches in a plurality of directions. When an image is formed on only one side of the paper P, it is discharged as it is onto the discharge tray 17 by the discharge roller 15.

  On the other hand, when images are formed on both sides of the sheet P, a part of the sheet P that has passed through the fixing device 7 is once projected from the discharge roller 15 to the outside of the apparatus. Thereafter, the paper P is distributed to the paper transport path 18 by the branching section 14 by rotating the discharge roller 15 in the reverse direction, and is transported again to the secondary transfer roller 9 with the image surface reversed. Examples of the secondary transfer roller 9 include a structure in which a foam layer (thickness 7.0 mm) made of EPDM rubber is formed as a roller body around a metal shaft (diameter 10 mm). Then, after the next image formed on the intermediate transfer belt 8 is transferred to the surface of the paper P where the image is not formed by the secondary transfer roller 9 and conveyed to the fixing device 7 to fix the toner image, It is discharged to the discharge tray 17.

  A density detection sensor 35 is disposed on the downstream side of the image forming unit Pd and the upstream side of the secondary transfer roller 9. The density detection sensor 35 irradiates the reference image formed on the intermediate transfer belt 8 in the image forming portions Pa to Pd with measurement light, and detects the amount of reflected light from the reference image. The detection result is transmitted to the control unit 90 described later as a light reception output signal. As the density detection sensor 35, an optical sensor provided with a light emitting element composed of an LED or the like and a light receiving element composed of a photodiode or the like is generally used. When measuring the darkness of the reference image, when the measurement light is sequentially emitted from the light emitting element to the reference image on the intermediate transfer belt 8, the measurement light is received as light reflected by the toner and light reflected by the belt surface. Incident on the element.

  When the toner adhesion amount is large, the reflected light from the belt surface is blocked by the toner, so that the light reception amount of the light receiving element is reduced. On the other hand, when the adhesion amount of toner is small, conversely, the amount of reflected light from the belt surface increases, resulting in an increase in the amount of light received by the light receiving element. Therefore, the toner adhesion amount (image density) of the reference image of each color is detected based on the output value of the received light signal based on the received reflected light amount, and the exposure value and the development bias characteristic value are compared with a predetermined reference density. By adjusting, density correction is performed for each color.

  Since the density detection sensor 35 needs to strictly define the distance to the reference image, which is a measurement object, as shown in FIG. 1, the density detection sensor 35 is provided with a driving roller 11 having a small distance variation to the surface of the intermediate transfer belt 8. It is arranged at a position facing each other.

  The density detection sensor 35 may be disposed at another position where the reference image on the intermediate transfer belt 8 can be detected. For example, when the density detection sensor 35 is disposed on the downstream side of the secondary transfer roller 9, the image forming units Pa to. There is a possibility that the time from when the reference image is formed by Pd to when the density detection is performed becomes longer, and when the reference image comes into contact with the secondary transfer roller 9, the surface state of the reference image may change. Therefore, as shown in FIG. 1, it is preferable that the intermediate transfer belt 8 is disposed downstream of the image forming unit Pd and upstream of the contact position of the secondary transfer roller 9 with respect to the moving direction of the intermediate transfer belt 8.

  FIG. 2 is an enlarged view of the vicinity of the magenta image forming portion Pa in FIG. Since the image forming units Pb to Pd have basically the same configuration, description thereof is omitted. Around the photosensitive drum 1a, a charger 2a, a developing device 3a, and a cleaning device 5a are arranged along the drum rotation direction (counterclockwise in FIG. 2), and the primary transfer roller 6a is sandwiched between the intermediate transfer belt 8. Is arranged. Examples of the primary transfer roller 6a include a structure in which a foam layer (thickness 6.0 mm) made of EPDM rubber is formed as a roller body around a metal shaft (diameter 8 mm).

  A belt cleaning device 19 having a brush roller 19a facing the driven roller 10 with the intermediate transfer belt 8 interposed therebetween is disposed upstream of the photosensitive drum 1a in the rotation direction of the intermediate transfer belt 8. The brush roller 19a is rotationally driven in the counter direction on the contact surface with the intermediate transfer belt 8 at a linear speed higher than the linear speed of the intermediate transfer belt 8 (here, 1.2 times).

  The charger 2 a includes a charging roller 21 that contacts the photosensitive drum 1 a and applies a charging bias to the drum surface, and a charging cleaning roller 23 for cleaning the charging roller 21. The developing device 4a is a touch-down developing type having two stirring and conveying screws 25, a magnetic roller 27, and a developing roller 29. The developing roller 29 has a developing bias having the same polarity (positive) as the toner charging polarity. Applied to cause the toner to fly on the drum surface.

  The cleaning device 5 a includes a rubbing roller (abrasive member) 30, a cleaning blade 31, and a collection spiral 33. The rubbing roller 30 is pressed against the photosensitive drum 1a with a predetermined pressure, and is driven to rotate in the same direction on the contact surface with the photosensitive drum 1a by a cleaning motor (see FIG. 4). Is controlled faster than the linear speed of the photosensitive drum 1a (1.2 times here). Examples of the rubbing roller 30 include a structure in which a foam layer made of EPDM rubber and having an Asuka C hardness of 55 ° is formed as a roller body around a metal shaft. The material of the roller body is not limited to EPDM rubber, but may be rubber or foam rubber body of other materials, and those having an Asuka C hardness in the range of 10 to 90 ° are preferably used.

  A cleaning blade 31 is fixed in contact with the photosensitive drum 1a on the surface of the photosensitive drum 1a downstream of the contact surface with the rubbing roller 30 in the rotation direction. As the cleaning blade 31, for example, a polyurethane rubber blade having a JIS hardness of 78 ° is used, and is attached at a predetermined angle with respect to the tangential direction of the photosensitive member at the contact point. The material, hardness, dimensions, the amount of biting into the photosensitive drum 1a, the pressure contact force, and the like of the cleaning blade 31 are appropriately set according to the specifications of the photosensitive drum 1a.

  The residual toner removed from the surface of the photosensitive drum 1 a by the rubbing roller 30 and the cleaning blade 31 is discharged to the outside of the cleaning device 5 a as the collection spiral 33 rotates. As the toner used in the present invention, an external additive (abrasive) selected from silica, titanium oxide, strontium titanate, alumina and the like is embedded on the surface of the toner particles and held so as to partially protrude on the surface. And those having an external additive electrostatically attached to the toner surface.

  Next, the configuration of the intermediate transfer belt 8 will be described in detail. FIG. 3 is a schematic cross-sectional view showing a configuration example of the intermediate transfer belt of the present invention. The intermediate transfer belt 8 is a conductive belt having a three-layer structure including a base material layer 80, an elastic layer 81, and a coat layer 83, and the coat layer 83 is in contact with the photosensitive drums 1a to 1d (see FIG. 1). The base material layer 80 becomes a basic material constituting the intermediate transfer belt 8, imparts a predetermined rigidity, withstands processing conditions when the elastic layer 81 and the coat layer 83 are laminated, and further manufactures the intermediate transfer belt 8. In this case, it is preferable that the material is excellent in workability, heat resistance, slipperiness, and other physical properties. As the material of the base material layer 80, for example, PVDF (polyvinylidene fluoride), polyimide resin, or the like is preferably used.

  The elastic layer 81 imparts elasticity to the intermediate transfer belt 8 to prevent image dropout due to stress concentration. When an elastic belt including an elastic layer 81 of at least 100 μm or more is used as the intermediate transfer belt 8, the contact nip between the drum and the belt is easy to stabilize and uniform polishing is preferable. As a material of the elastic layer 81, for example, hydrin rubber, chloroprene rubber, polyurethane rubber or the like is used. The coat layer 83 protects the elastic layer 81. As a material of the coat layer 83, acrylic, silicon, fluororesin, or the like is used.

In addition, the structure which does not contain the base material layer 80, the structure which contains other layers other than the base material layer 80, the elastic layer 81, and the coat layer 83 may be sufficient, and not only a laminated structure but only the elastic layer 81 is sufficient. A layer structure may be adopted. The surface resistivity of the intermediate transfer belt 8 is preferably 1 × 10 ¹⁰ to 1 × 10 ¹² Ω · cm, and the surface hardness is preferably about 10 to 60 in terms of MD-1 hardness.

As a specific configuration of the intermediate transfer belt 8 used in the present invention, for example, a base layer 80 made of PVDF resin having a thickness of 0.1 mm, an elastic layer 81 made of NBR rubber having a thickness of 0.3 mm, and a thickness An endless belt having a three-layer structure having a surface resistance value of 5 × 10 ¹⁰ Ω · cm, in which a coating layer 83 made of PTFE (polytetrafluoroethylene) having a thickness of 10 μm is laminated.

  Next, the control path of the image forming apparatus of the present invention will be described. FIG. 4 is a block diagram showing an example of a control path used in the image forming apparatus of the present invention. In addition, since various controls of each part of the apparatus are performed when the color printer 100 is used, the control path of the entire color printer 100 becomes complicated. Therefore, here, a portion of the control path that is necessary for the implementation of the present invention will be mainly described.

  The control unit 90 includes a central processing unit (CPU) 91 as a central processing unit, a read only memory (ROM) 92 that is a read-only storage unit, a random access memory (RAM) 93 that is a read / write storage unit, A plurality of (two in this case) that transmit control signals to and receive input signals from the operation unit 50, such as a temporary storage unit 94 that stores image data and the like, a counter 95, and each device in the color printer 100. At least an I / F (interface) 96 is provided. Further, the control unit 90 can be arranged at an arbitrary location inside the apparatus main body.

  The ROM 92 stores control programs for the color printer 100, data necessary for control, and the like that are not changed during use of the color printer 100. The RAM 93 stores necessary data generated during the control of the color printer 100, data temporarily required for the control of the color printer 100, and the like. The counter 95 adds up the number of printed sheets and counts it.

  The control unit 90 transmits a control signal from the CPU 91 to the respective units and devices in the color printer 100 through the I / F 96. In addition, a signal indicating the state and an input signal are transmitted from each part or device to the CPU 91 through the I / F 96. Examples of the parts and devices controlled by the control unit 90 include, for example, the image forming units Pa to Pd, the exposure device 4, the primary transfer rollers 6a to 6d, the fixing device 7, the intermediate transfer unit 37, the secondary transfer roller 9, and belt cleaning. Examples of the apparatus 19 include an intermediate transfer unit 37, an intermediate transfer pressing / releasing operation unit 39, an image input unit 40, a motor control circuit 41, a bias control circuit 50, and an operation unit 60.

  The intermediate transfer unit 37 is formed by unitizing the primary transfer rollers 6a to 6d, the intermediate transfer belt 8, the driven roller 10, the driving roller 11, the belt cleaning device 19, and the tension roller 20 (all of which are shown in FIG. 1). As will be described later, when determining whether or not the intermediate transfer unit 37 is in the initial state, an IC memory 38 capable of writing / reading the use history information of the intermediate transfer unit 37 is attached. The intermediate transfer pressing / releasing operation unit 39 presses the primary transfer rollers 6a to 6d against the photosensitive drums 1a to 1d independently of each other with a predetermined pressure in accordance with a control signal from the control unit 90 to release the pressing.

  The image input unit 40 is a receiving unit that receives image data transmitted to the color printer 100 from a personal computer or the like. The image signal input from the image input unit 40 is converted into a digital signal and then sent to the temporary storage unit 94.

  The motor control circuit 41 is connected to the drum motor 42, the development motor 43, the cleaning motor 44, and the belt drive motor 45, and controls the driving of the motors 42 to 46 by an output signal from the control unit 90.

  Each of these motors 42 to 46 is controlled by a control signal from a motor control circuit 41, the drum motor 42 is for the photosensitive drums 1a to 1d, and the developing motor 43 is for the stirring and conveying screw 25, the magnetic roller 27 in the developing devices 3a to 3d, The developing roller 29, the cleaning motor 44 drive the rubbing roller 30 in the cleaning devices 5a to 5d, and the belt drive motor 45 drives the intermediate transfer belt 8 and the secondary transfer roller 9 at predetermined linear speeds, respectively.

  Further, four drum motors 42 are arranged corresponding to the respective photosensitive drums 1a to 1d, and the photosensitive drums 1a to 1d can be driven independently. A DC motor is used as the drum motor 42, and a stepping motor is used as the belt drive motor 45.

  The brush roller 19a of the belt cleaning device 19 is connected to a spiral drive motor (not shown) that rotationally drives the recovery spiral 33 in the cleaning devices 5a to 5d. It is the same drive series.

  The bias control circuit 50 is connected to the charging bias power source 51, the developing bias power source 52, the transfer bias power source 53, and the belt cleaning bias power source 54, and operates each of these power sources by an output signal from the control unit 90. Each of these power sources 51 to 54 is controlled by a control signal from the bias control circuit 50, the charging bias power source 51 is to the charging roller 21 in the chargers 2a to 2d, and the developing bias power source 52 is to the magnetic roller 27 in the developing devices 3a to 3d. The transfer bias power source 53 applies a predetermined bias to the primary transfer rollers 6a to 6d and the secondary transfer roller 9, and the belt cleaning bias power source 54 applies a predetermined bias to the belt cleaning roller 19a. The primary transfer bias applied to the primary transfer rollers 6a to 6d is controlled to a constant current of, for example, −15 μA for each color, and the secondary transfer bias applied to the secondary transfer roller 9 is controlled to a constant current of, for example, −30 μA. .

  The operation unit 60 is provided with a liquid crystal display unit 61, LEDs 62 for indicating various states, and a numeric keypad 63. The user operates the operation unit 60 to input instructions, thereby setting various settings of the color printer 100. Then, various functions such as image formation are executed. The liquid crystal display unit 61 displays the status of the color printer 100, displays the image forming status and the number of copies, and can be used as a touch panel to perform various settings such as functions such as double-sided printing and black-and-white reversal, magnification setting, and density setting. It has become.

  In addition, the operation unit 60 includes a start button for instructing the user to start image formation, a stop / clear button used when the image formation is stopped, and various settings of the color printer 100 when making the default settings. A reset button or the like to be used is provided.

  By the way, when the image forming apparatus 100 is in the initial state or immediately after the replacement of the intermediate transfer unit 37, the surface friction coefficient of the intermediate transfer belt 8 is high. In such a state, the adhesion force of the toner to the intermediate transfer belt 8 is increased and the transferability to the recording medium is deteriorated. As a result, so-called hollowing out phenomenon and image fluttering occur. Further, since the winding property (tackiness) to the photosensitive drums 1a to 1d is also increased, the belt is expanded and contracted between the photosensitive drums 1a to 1d, and color misregistration is likely to occur.

  Therefore, in the image forming apparatus of the present invention, the toner adhesion mode in which the toner is deposited on the intermediate transfer belt 8 is executed. Specifically, the photosensitive drums 1a to 1d and the intermediate transfer belt 8 are driven with a linear velocity difference, and in this state, halftone images M to K as shown in FIG. 5 are formed on the photosensitive drums 1a to 1d. The intermediate transfer belt 8 is formed and transferred to the entire image formable width. The length of the halftone images M to K in the belt circumferential direction (the vertical direction in FIG. 5) is not particularly limited, but is set to, for example, the length of one drum circumference. The number of times of transfer (application) of the halftone images M to K on the surface of the intermediate transfer belt 8 in the toner adhesion mode is not particularly limited, but at least about 5 times is necessary to sufficiently attach the external additive. is there.

  As a result, the halftone images M to K are rubbed against the belt surface, and the toner and the external additive contained in the toner adhere to the surface of the intermediate transfer belt 8. The halftone images M to K are removed by the belt cleaning device 19. However, since the external additive has a stronger adhesive force than the toner and remains on the belt surface, the belt surface is whitened as shown in FIG. (Gloss value) decreases. Since the surface friction coefficient of the intermediate transfer belt 8 is reduced as compared with the initial state due to adhesion of the external additive, the above-described problems can be effectively suppressed.

  Further, as a method of giving a linear velocity difference between the photosensitive drums 1a to 1d and the intermediate transfer belt 8, a method of decelerating one of the photosensitive drums 1a to 1d or the intermediate transfer belt 8 and a method of accelerating one of them. A method is considered. However, when accelerating any one of the photosensitive drums 1 a to 1 d or the intermediate transfer belt 8, the load on the drum motor 42 or the belt driving motor 45 increases, so that the photosensitive drums 1 a to 1 d and the intermediate transfer belt 8 are The structure which decelerates either one is preferable.

  7 and 8 show the relationship between the toner adhesion mode execution time and the gloss (gloss value) of the surface of the intermediate transfer belt when the linear speed ratio of the photosensitive drum to the intermediate transfer belt is changed stepwise. 6 is a graph showing the relationship between the toner adhesion mode execution time and the dynamic friction coefficient of the intermediate transfer belt surface. FIG. 9 is a graph showing the relationship between the glossiness (gloss value) of the intermediate transfer belt surface and the dynamic friction coefficient of the intermediate transfer belt surface.

  As shown in FIG. 7, the gloss value when the toner adhesion mode is continued for 5 minutes is 14.8 when the ratio of the linear velocity of the photosensitive drum to the belt is 100% (data series of ■). As the speed ratio increases to 95% (data series of ◆), 90% (data series of ▲), 70% (data series of ○), and 50% (data series of □), the gross value increases. They decreased to 13.5, 11.6, 9.3, and 7.7, respectively.

  As shown in FIG. 8, the dynamic friction coefficient of the surface of the intermediate transfer belt when the toner adhesion mode is continued for 5 minutes is 0. When the linear speed ratio of the photosensitive drum to the belt is 100% (data series of ■). The belt speed ratio is 95% (data series of ◆), 90% (data series of ▲), 70% (data series of ○), and 50% (data series of □). As it increased, the dynamic friction coefficients decreased to 0.266, 0.246, 0.224, and 0.209, respectively. That is, as shown in FIG. 9, the glossiness (gloss value) of the surface of the intermediate transfer belt is proportional to the dynamic friction coefficient, and the dynamic friction coefficient decreases as the gloss value decreases.

  FIG. 10 is a graph showing the relationship between the dynamic friction coefficient on the surface of the intermediate transfer belt and the image roughness. Note that the image mottle on the vertical axis is a solid area spot characterized by a large number of spots and irregular appearance in the solid area of the solid image, and is measured by a method defined in ISO 13660.

  As shown in FIG. 10, the image fluctuation and the dynamic friction coefficient correlate, and the fluctuation becomes significant as the dynamic friction coefficient increases. It can also be seen that by setting the dynamic friction coefficient to 0.3 or less, the image blur can be suppressed to an allowable value of 0.6 or less. That is, by performing the toner adhesion mode and reducing the surface friction coefficient of the intermediate transfer belt 8, it is possible to effectively suppress image blurring. Although not described here, the same correlation as in FIG. 10 is confirmed for the dynamic friction coefficient on the surface of the intermediate transfer belt and the void phenomenon.

  7 and 8 that the dynamic friction coefficient decreases faster as the linear velocity difference between the photosensitive drums 1a to 1d with respect to the intermediate transfer belt 8 is increased. This is because the toner is rubbed against the surface of the intermediate transfer belt 8 by the friction with the photosensitive drums 1a to 1d, and the adhesion of the external additive is increased. Accordingly, the linear speed ratio of the intermediate transfer belt 8 to the photosensitive drums 1a to 1d is set to 90% or less, although it depends on the initial value of the dynamic friction coefficient on the surface of the intermediate transfer belt 8 and the added amount of the external toner additive.

  However, if the difference between the linear speeds of the photosensitive drums 1a to 1d with respect to the intermediate transfer belt 8 becomes too large, the drive torque of the intermediate transfer belt 8 also increases, and an excessive load is applied to the belt drive motor 45 (see FIG. 4) to rotate. There is a risk of disappearing. Further, the abrasion amount of the photosensitive layers of the photosensitive drums 1a to 1d is increased and the durability is lowered. Therefore, it is preferable that the linear speed ratio of the photosensitive drums 1a to 1d with respect to the intermediate transfer belt 8 is in the range of 30% to 70%.

  FIG. 11 is a flowchart showing a control example of the toner adhesion mode executed in the image forming apparatus according to the first embodiment of the present invention. The operation of each part of the apparatus in the toner adhesion mode will be described along the steps in FIG. 11 with reference to FIGS.

  First, when a new intermediate transfer unit 37 is attached to the apparatus main body by a user or a service person and a toner adhesion mode is selected (hereinafter referred to as a manual mode) by operating the operation panel 50 (step S1), the control unit 90 performs a motor operation. A control signal is transmitted to the control circuit 41, and driving of the drum motor 42, the developing motor 43, the cleaning motor 44, the belt driving motor 45, etc. is started (step S2). Next, the controller 90 decelerates the drum motor 42 to decelerate the linear speed of the photosensitive drums 1a to 1d (step S3). Thereby, a linear velocity difference is provided between the photosensitive drums 1 a to 1 d and the intermediate transfer belt 8.

  Next, a printing operation for forming toner images on the photosensitive drums 1a to 1d is started (step S4). Specifically, a control signal is transmitted from the control component 90 to the bias control circuit 50, and a charging bias is applied from the charging bias power source 51 to the chargers 2a to 2d, so that the surfaces of the photosensitive drums 1a to 1d are made uniform. It is charged and then irradiated with light by the exposure device 4 to form electrostatic latent images on the photosensitive drums 1a to 1d. Further, toner is supplied onto the photosensitive drums 1a to 1d by applying a developing bias from the developing bias power source 52 to the developing rollers 29 of the developing devices 3a to 3d, and the toner images of the respective colors are attached to the electrostatic latent images. Is formed.

  In this state, a primary transfer bias is applied from the transfer bias power source 53 to the primary transfer rollers 6a to 6d to output an image pattern as shown in FIG. 5 on the surface of the intermediate transfer belt 8 (step S5). The output of the image pattern is repeated a predetermined number of times, and 1 is added to the number N of outputs stored in the counter 95 for each output (step S6). At this time, a transfer reverse bias having the same polarity as the toner is applied to the secondary transfer roller 9 from the transfer bias power supply 53, and a cleaning bias having a reverse polarity to the toner is applied to the brush roller 19 a of the belt cleaning device 19 from the belt cleaning bias power supply 54. Therefore, the image pattern on the intermediate transfer belt 8 is collected by the brush roller 19a without adhering to the secondary transfer roller.

  Then, it is determined whether or not the predetermined number of times (here, 20 times) of output has been completed (step S7), and when the predetermined number of times has been completed, the control unit 90 transmits a control signal to the bias control circuit 50 for printing. The operation is terminated (step S8), a control signal is transmitted to the motor control circuit 41, and the driving of the apparatus is stopped (step S9). Thereafter, “READY” is displayed on the liquid crystal display unit 61 (step S10), and the toner adhesion mode is terminated.

  If the toner adhesion mode is executed by the above control, the toner external additive uniformly adheres to the transferable area of the intermediate transfer belt 8 as shown in FIG. 6, and the surface friction coefficient of the intermediate transfer belt 8 is lowered. As a result, the transfer performance from the intermediate transfer belt 8 to the recording medium is improved, and it is possible to effectively suppress the image dropout phenomenon and the unevenness. Further, the tack property (winding property) with respect to the photosensitive drums 1a to 1d is also reduced, so that the slipping property between the intermediate transfer belt 8 and the photosensitive drums 1a to 1d is improved, and the expansion and contraction of the intermediate transfer belt 8 is also suppressed. Color misregistration is less likely to occur.

  Further, the intermediate transfer belt 8 having the elastic layer 81 on the surface as shown in FIG. 3 has an adverse effect due to the characteristics due to the elastic force even when the thickness of the recording medium and the unevenness of the surface are different. Covers and exhibits good transfer performance regardless of the type of recording medium, but the surface friction coefficient is relatively high, and there is a concern that the above-described image defects are likely to occur. Therefore, by combining such an intermediate transfer belt 8 and the image forming apparatus of the present invention capable of executing the toner adhesion mode, the surface friction coefficient of the intermediate transfer belt 8 can be reduced and the transfer performance can be further improved. it can.

  The photosensitive drums 1a to 1d, in which the photosensitive layer is formed of amorphous silicon, are widely used because of their high hardness, excellent wear resistance, and long life. There is also a problem that discharge products adhere to the surface and the surface friction coefficient increases. Therefore, by combining the photosensitive drums 1a to 1d with the image forming apparatus of the present invention capable of executing the toner adhesion mode, the photosensitive drums 1a to 1d are intermediated via an external additive having a polishing effect. Since the transfer belt 8 is rubbed, it becomes an effective drum polishing system that can remove deposits on the drum surface in a short time and reduce the increase in the surface friction coefficient.

  Note that the control shown in FIG. 11 is merely an example, and can be appropriately changed according to the specifications of the apparatus. For example, in the control of FIG. 11, the linear speed of the photosensitive drums 1 a to 1 d is reduced to create a linear speed difference between the photosensitive drums 1 a to 1 d and the intermediate transfer belt 8, but the photosensitive drums 1 a to 1 d. Instead, the linear speed of the intermediate transfer belt 8 may be reduced.

  FIG. 12 is a flowchart illustrating a control example of the toner adhesion mode executed in the image forming apparatus according to the second embodiment of the present invention. The operation of each unit in the toner adhesion mode will be described along the steps of FIG. 12 with reference to FIGS. In this embodiment, in addition to the manual mode selected by the operation of the user or service person, it is determined whether or not the intermediate transfer unit 37 is in the initial state. If it is in the initial state, the toner adhesion mode is automatically set. It has an auto mode to execute.

  First, when the toner adhesion mode is selected, the control unit 90 determines whether or not the auto mode is selected (step S1). When the auto mode is selected, the use history stored in the IC memory 38 attached to the intermediate transfer unit 37 is read to determine whether or not the intermediate transfer unit 37 is in the initial state (step S2). . If the intermediate transfer unit 37 is in the initial state, the control unit 90 transmits a control signal to the motor control circuit 41 to start driving the apparatus (step S3).

  Next, the control unit 90 transmits a control signal to the motor control circuit 41 to decelerate only a part of the photosensitive drums 1a to 1d (here, the photosensitive drum 1d) (step S4). Thereby, a linear velocity difference is provided between the photosensitive drum 1d and the intermediate transfer belt 8. Next, a printing operation for forming a toner image on the photosensitive drum 1d is started (step S5).

  In this state, a first adhesion process is performed in which a primary transfer bias is applied to the primary transfer roller 6d to output a black image pattern on the surface of the intermediate transfer belt 8 (step S6). The output of the image pattern is repeated a predetermined number of times, and 1 is added to the number N of outputs stored in the counter 95 for each output (step S7). During steps S5 to S7, the other photosensitive drums 1a to 1c rotate at the same linear speed as the intermediate transfer belt 8, and the printing operation and the image pattern output are not performed. The black image pattern output at this time is formed longer in the belt circumferential direction than the halftone image K shown in FIG. The length in the belt circumferential direction is determined in consideration of the recovery capability of the belt cleaning device 19 and the toner replenishment capability to the developing device 3d.

  Then, it is determined whether or not the predetermined number of times (here, 15 times) of output has been completed (step S8). When the predetermined number of times has been completed, the control unit 90 transmits a control signal to the motor control circuit 41 to decelerate. The number of photosensitive drums to be increased is increased (step S9). Here, the remaining three photosensitive drums 1a to 1c are decelerated in addition to the photosensitive drum 1d. Then, a toner image is formed on the photosensitive drums 1a to 1d, and a second adhesion process is performed in which a primary transfer bias is applied to the primary transfer rollers 6a to 6d to output an image pattern of four colors on the surface of the intermediate transfer belt 8. (Step S10). The output of the image pattern is repeated a predetermined number of times, and 1 is added to the number N of outputs stored in the counter 95 for each output (step S11).

  Then, it is determined whether or not the predetermined number of times (here, 10 times) of output has been completed (step S12). When the predetermined number of times has been completed, the control unit 90 transmits a control signal to the bias control circuit 50 for printing. The operation is terminated (step S13), a control signal is transmitted to the motor control circuit 41, and the driving of the apparatus is stopped (step S14). Thereafter, “READY” is displayed on the liquid crystal display unit 61 (step S15), and the toner adhesion mode is terminated. If the intermediate transfer unit 37 is not in the initial state in step S2, the toner adhesion mode is not executed, and only the apparatus is warmed up. Then, “READY” is displayed on the liquid crystal display unit 61 (step S15). Exit.

  On the other hand, if the manual mode is selected in step S1, it is next determined whether or not the intermediate transfer unit is in the initial state (step S16). If it is in the initial state, the process proceeds to step S3, where the first attachment is performed. A process and a 2nd adhesion process are performed continuously (Steps S3-S15). If the unit is not in the initial state in step S16, the driving of the apparatus is started and the photosensitive drums 1a to 1d for all four colors are decelerated to give a linear velocity difference with the intermediate transfer belt 8 in step S10. Then, only the second adhesion process is executed (steps S10 to S15).

  If the toner adhesion mode is executed by the above-described control, it is possible to effectively suppress an image dropout phenomenon, image fluttering, and color misregistration due to expansion / contraction of the intermediate transfer belt, as in the first embodiment. Further, since it is possible to automatically determine whether or not the intermediate transfer unit 37 (intermediate transfer belt 8) is in the initial state, there is no possibility of forgetting to execute the toner adhesion mode when the intermediate transfer unit 37 is replaced.

  Incidentally, when the intermediate transfer belt 8 is in the initial state, the surface friction coefficient is high, and the tackiness with the photosensitive drums 1a to 1d is also high. In this state, if driving is performed with a difference in linear velocity between the plurality of photosensitive drums, the driving torque of the intermediate transfer belt 8 becomes large and exceeds the rated torque of the belt driving motor 45 to drive the motor. There is also a possibility that it will not. Therefore, as in the present embodiment, when the intermediate transfer belt 8 is in the initial state, only the photosensitive drum (one photosensitive drum 1d in this case) of any one color (here, the photosensitive drum 1d) is decelerated to execute the first attachment process. Then, after the external additives adhere to some extent, the remaining three color photosensitive drums 1a to 1c are decelerated and the second adhesion step is executed, so that the driving torque of the intermediate transfer belt 8 in the toner adhesion mode is reduced and smoothed. And the external additive can be attached to the surface of the intermediate transfer member in a short time with a small amount of toner.

  When the manual mode is selected, if the intermediate transfer belt 8 is in the initial state, the first and second adhesion steps are executed by the same procedure as in the auto mode, and the external additive is applied to the surface of the intermediate transfer belt 8. Can be attached smoothly. In addition, when the intermediate transfer belt 8 is not in the initial state, the external additive can be quickly and efficiently attached to the surface of the intermediate transfer belt 8 by executing the second attaching step from the beginning.

  In the first attaching step of decelerating the photosensitive drum 1d of one color, the other photosensitive drums 1a to 1c are accelerated to have a linear velocity difference in a direction that assists driving of the intermediate transfer belt 8. Further, the driving of the intermediate transfer belt 8 becomes smoother.

  FIG. 13 is a flowchart illustrating a control example of the toner adhesion mode executed in the image forming apparatus according to the third embodiment of the present invention. With reference to FIGS. 1 to 6, the operation of each unit in the toner adhesion mode will be described along the steps of FIG. 13. In this embodiment, it is determined whether or not the intermediate transfer unit 37 is in the initial state (step S2). If the intermediate transfer unit 37 is in the initial state, the intermediate transfer pressing / releasing operation unit 39 starts driving the apparatus (step S3). The pressure contact state of any of the three color photosensitive drums (here, the photosensitive drums 1a to 1c) to the intermediate transfer belt 8 is released (step S4).

  Then, only the photosensitive drum 1d pressed against the intermediate transfer belt 8 is decelerated (step S5), and an image pattern is output (transferred) a predetermined number of times (here, 15 times) to the intermediate transfer belt 8 by the photosensitive drum 1d. After performing the first attaching step (steps S6 to S9), the photosensitive drums 1a to 1d of all four colors are brought into pressure contact with the intermediate transfer belt 8 in a decelerated state, and an image pattern of a predetermined number of times (here, 10 times) is formed. It is supposed to perform the 2nd adhesion process which performs output (Steps S10-S14). Other controls are the same as those in the second embodiment shown in FIG.

  If the toner adhesion mode is executed by the above-described control, only one of the photosensitive drums (here, the photosensitive drum 1d) is pressed against the intermediate transfer belt 8 when the intermediate transfer belt 8 is in the initial state. The first adhesion step is executed in a decelerated state, and after the external additive has adhered to some extent, the remaining three color photosensitive drums 1a to 1c are pressed in the decelerated state, and the second attachment step is executed. Similar to the second embodiment, the driving torque of the intermediate transfer belt 8 in the toner adhesion mode can be reduced and smoothly driven, and the external additive can be adhered to the surface of the intermediate transfer member with a small amount of toner in a short time. be able to.

  By the way, the external additive once adhered to the intermediate transfer belt 8 has a weak adhesive force, and when the toner transferred to the surface of the intermediate transfer belt 8 is collected by the belt cleaning device 19, it adheres to the toner. There are things that will be collected along with it. Therefore, when the same image pattern is repeatedly output on the intermediate transfer belt 8, the increase in the amount of external additive attached to the surface of the intermediate transfer belt 8 becomes moderate.

  FIG. 14 is a graph showing the relationship between the belt driving time and the glossiness (gross value) of the belt surface. From FIG. 10, since the glossiness of the belt surface where the image roughness is within the allowable range (the dynamic friction coefficient is 0.3 or less) is gloss 16, the target value of the gloss value is set to 16, and the solid image pattern is output four times. When only aging (belt idling) is performed, when a halftone image pattern is repeatedly output, and when a halftone image pattern is repeatedly output after 60 seconds of aging, it is required to attenuate to the target gloss 16 Time was compared.

  As shown in FIG. 14, if a halftone image is repeatedly output after outputting a solid image, the attenuation rate of the glossiness decreases, and it takes 80 seconds for the glossiness to attenuate to gloss 16 (indicated by the bold line in the figure). (Indicated by ▲ in the figure). This is because a part of the external additive adhering to the belt surface adheres to and peels off from the toner to be applied. In addition, when only the belt is rotated after output of the solid image (indicated by ■ in the figure), the glossiness decay rate becomes the largest, and the glossiness decays to gloss 16 in about 50 seconds, but the toner adheres. When normal image formation is performed after the mode is completed, there is a possibility that uneven peeling (attachment unevenness) of the external additive occurs between a portion where the image is present and a portion where the image is absent.

  On the other hand, when the halftone image pattern is repeatedly output after 60 seconds of aging (indicated by □ in the figure), since the external additive is sufficiently adhered and glossiness is attenuated by the idling of 60 seconds, the halftone image is displayed. As in the case of repeated output, it attenuated to gross 16 in about 50 seconds. Thereafter, although the gloss value slightly increases due to the output of the halftone image, it is possible to suppress uneven peeling of the external additive during normal image formation by outputting the halftone image. That is, by combining the aging and the output of the halftone image, it is possible to achieve both the reduction of the gloss value (dynamic friction coefficient) on the surface of the intermediate transfer belt and the suppression of uneven adhesion of the external additive.

  FIG. 15 is a flowchart illustrating a toner adhesion mode control example executed in the image forming apparatus according to the fourth embodiment of the present invention. With reference to FIGS. 1 to 6, the operation of each unit in the toner adhesion mode will be described along the steps in FIG. 15. In this embodiment, when the intermediate transfer unit 37 is in the initial state, the pressure contact state of any three color photosensitive drums (here, the photosensitive drums 1a to 1c) to the intermediate transfer belt 8 is released (step S4). At the same time, the one-color photosensitive drum (here, the photosensitive drum 1d) that is in pressure contact is decelerated (step S5), and a first adhesion process is performed in which a solid image pattern is output a predetermined number of times (here, four times) ( Steps S6 to S9).

  Next, an idling process is performed in which the intermediate transfer belt 8 is idly rotated for 30 seconds while the photosensitive drum 1d is in a decelerating state (step S10). Thereafter, a second attachment step is performed in which all the photosensitive drums 1a to 1d of the four colors are brought into pressure contact with the intermediate transfer belt 8 in a decelerated state, and a solid image pattern is output a predetermined number of times (here, four times) (step S11). To S15). Next, an idling process is performed in which the intermediate transfer belt 8 is idly rotated for 30 seconds while the photosensitive drums 1a to 1d are in a decelerating state (step S16). Finally, the second adhesion process is executed again to output a halftone image pattern a predetermined number of times (here, 10 times) (steps S17 to S19). Other controls are the same as those in the third embodiment shown in FIG.

  If the toner adhesion mode is executed by the control described above, the surface of the intermediate transfer belt 8 is repeatedly slid by the photosensitive drums 1a to 1d by performing the idling process after outputting (transferring) the solid image pattern to the intermediate transfer belt 8. Because of rubbing, adhesion of the external additive to the intermediate transfer belt 8 is improved. In addition, the second adhesion process is executed again after the idling process to output a halftone image pattern with a low printing rate, so that the external additive having a low adhesion strength is adhered to the toner and collected, and a new external additive is recovered. The agent can be supplied to the intermediate transfer belt 8. Thereby, the adhesion amount and adhesion strength of the external additive can be increased efficiently, and the occurrence of uneven adhesion of the external additive during the subsequent normal image output can be prevented. The density of the halftone image is preferably about 10% to 20%.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the second to fourth embodiments, whether or not the intermediate transfer unit 37 is in the initial state is determined by reading use history information in the IC memory 38 attached to the intermediate transfer unit 37. Alternatively, it may be determined whether the intermediate transfer unit 37 is in the initial state using the reflected light from the surface of the intermediate transfer belt 8 measured by the density detection sensor 35.

  The present invention is not limited to the tandem type color image forming apparatus as shown in FIG. 1, but can be applied to other image forming apparatuses using an intermediate transfer member, such as a rotary type color image forming apparatus.

  The present invention is applicable to an image forming apparatus using an intermediate transfer member, and executes a toner adhesion mode in which an image is transferred with a difference in linear velocity between the intermediate transfer member and the image carrier during non-image formation. It is. As a result, the surface friction coefficient of the intermediate transfer member is reduced, so that the image dropout phenomenon and the unevenness can be effectively suppressed. As a method for giving a difference in linear velocity between the intermediate transfer member and the image carrier, a method of decelerating either the intermediate transfer member or the image carrier is preferable.

  Further, by automatically determining whether or not the toner adhesion mode needs to be executed according to whether or not the intermediate transfer member is in the initial state, it is possible to reliably prevent the toner adhesion mode from not being executed or being excessively executed. .

1a to 1d Photosensitive drum (image carrier)
2a to 2d Charger 3a to 3d Developing device 4 Exposure device 5a to 5d Cleaning device 6a to 6d Primary transfer roller 7 Fixing device 8 Intermediate transfer belt (intermediate transfer member)
9 Secondary transfer roller 19 Belt cleaning device 37 Intermediate transfer unit 38 IC memory 41 Motor control circuit 50 Bias control circuit 60 Operation unit 90 Control unit (control means)
100 color printer Pa to Pd image forming unit

Claims (9)

A plurality of image bearing members on which an electrostatic latent image is formed, and a developing device that forms a toner image corresponding to the electrostatic latent image by supplying toner containing an external additive to the surface of the image bearing member. An image forming unit;
An endless intermediate transfer member to which a toner image formed on the image carrier in the image forming unit is primarily transferred;
In a color image forming apparatus comprising:
By transferring a toner image formed on the image carrier a predetermined number of times onto the intermediate transfer member with a linear velocity difference between the image carrier and the intermediate transfer member during non-image formation. A toner attachment mode in which toner is attached to the entire image formable width of the intermediate transfer member can be executed;
The toner adhesion mode includes a first adhesion step in which a toner image is transferred onto the intermediate transfer member in a state where a linear velocity difference is provided between a part of the plurality of image carriers and the intermediate transfer member. ,
After the toner image formed on the image carrier in the first attaching step is transferred to the entire image formable width of the intermediate transfer member, a linear velocity difference is generated between the image carrier and the intermediate transfer member. An idling process in which driving is continued for a predetermined time in a standing state,
After the idling step, the image carrier having a linear velocity difference between the intermediate transfer member and the intermediate transfer member is increased stepwise to transfer the toner image onto the intermediate transfer member. A second attaching step to be performed;
An image forming apparatus comprising:   During the toner adhesion mode, the linear speed of the image carrier used for transferring the toner image is driven at a slower linear speed than the intermediate transfer body, and the image carrier that is not used for transferring the toner image is driven to the intermediate transfer The image forming apparatus according to claim 1, wherein the body is driven at a high linear velocity. In the first attaching step, a toner image is transferred onto the intermediate transfer member in a state where a part of the plurality of image carriers is in contact with the intermediate transfer member, and in the second attaching step, 2. The image forming apparatus according to claim 1, wherein the toner image is transferred by gradually increasing the number of image carriers to be brought into contact with the intermediate transfer member. The image forming apparatus according to claim 1 or claim 3, characterized in that the said 70% to 30% linear velocity ratio of the intermediate transfer member below with respect to the image bearing member in the toner adhesion mode. The image forming according to the second deposition step, in any one of claims 1 to 4 wherein the concentration of the toner image transferred to the intermediate transfer member is stepwise reduced, characterized in that repeatedly executes a plurality of times apparatus. 6. The control unit according to claim 5, further comprising a control unit that determines whether or not to execute the toner adhesion mode depending on whether or not an external additive is not adhered to the intermediate transfer member. Image forming apparatus. The toner adhesion mode includes an auto mode that is automatically executed depending on whether the intermediate transfer member is in an initial state when the apparatus is turned on or the intermediate transfer member is replaced, and the intermediate transfer member is in an initial state. A manual mode that is manually executed at an arbitrary timing regardless of whether the intermediate transfer member is not in an initial state in the manual mode, and the control unit executes only the second attachment step. The image forming apparatus according to claim 6 .   The image forming apparatus according to claim 1, wherein the intermediate transfer member is a laminate including an elastic layer.   The image forming apparatus according to claim 1, wherein the image carrier is an amorphous silicon photoconductor.