JP2016161850A - Transfer device, image forming apparatus, and transfer control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve high transferability to a recess part of a sheet.SOLUTION: A transfer device comprises: a first transfer member that carries a toner image; a second transfer part that forms a transfer nip with the first transfer member; and a voltage application part that applies, to the second transfer member, a transfer bias having a voltage waveform including an AC component that alternately repeats a phase corresponding to a transfer voltage and a phase corresponding to a return voltage. In the voltage waveform, a voltage value changes in a plurality of stages in both phases; the absolute value of the voltage in the first stage is larger than the absolute value of the voltage in the second and subsequent stages; the voltage application time in the first stage is shorter than the total sum of the voltage application times in the second and subsequent stages.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a transfer device, an image forming apparatus, and a transfer control method.

  Among image forming apparatuses (printers, copiers, facsimiles, etc.) using electrophotographic process technology, belt transfer type image forming apparatuses are known in recent years. In the belt transfer system, the transfer belt is run so as to come into contact with the photosensitive drum, and the paper is conveyed in synchronization with the toner image formed on the photosensitive drum. A transfer voltage having a polarity (transfer polarity) opposite to the charging polarity of the toner is applied to the transfer belt, and the toner image on the photosensitive drum is transferred to a sheet by electrostatic attraction.

  Various types of paper can be used as the paper on which the toner image is transferred, but this is particularly low when transferring onto paper having irregularities or textures on the surface (hereinafter referred to as “rough paper”). It is conventionally known that when a voltage having a waveform in which a high alternating current component is superimposed on a direct current component (hereinafter referred to as “AC superimposed transfer”), transferability to a concave portion of a sheet can be improved. Such improvement in transfer performance is related to the fact that toner in an AC electric field formed by AC components reciprocates between the transfer belt and the paper. For example, in the image forming apparatus described in Patent Document 1, it is described that generation of so-called “white spots” is suppressed in a concave portion of a sheet by using an AC superimposed transfer technique.

JP2013-127599A

  However, in the technique described in Patent Document 1, although it is possible to prevent the entire concave portion of the paper from becoming white, there is a possibility that white spots may locally occur in the concave portion of the paper. In other words, the technique described in Patent Document 1 has a certain limit in improving the transferability of the paper to the concave portion.

  An object of the present invention is to provide a transfer device, an image forming apparatus, and a transfer control method capable of realizing high transferability to a concave portion of a sheet.

The transfer device according to the present invention is:
A first transfer member carrying a toner image;
A second transfer member that forms a transfer nip with the first transfer member;
A voltage applying unit that applies a transfer bias having a voltage waveform including an AC component that alternately repeats a phase corresponding to the transfer voltage and a phase corresponding to the return voltage to the second transfer member;
With
The voltage waveform has a voltage value that changes in a plurality of stages in any phase, the absolute value of the voltage of the first stage is larger than the absolute value of the voltage after the second stage, and the voltage application time of the first stage is 2 It is shorter than the total voltage application time after the stage.

An image forming apparatus according to the present invention includes:
The transfer apparatus is included.

The transfer control method according to the present invention includes:
A transfer control method for transferring a toner image to a sheet at a transfer nip by applying a transfer bias,
A control step of controlling a voltage application unit for applying the transfer bias,
The control step is a voltage waveform including an AC component that alternately repeats a phase corresponding to the transfer voltage and a phase corresponding to the return voltage, and the voltage value changes in a plurality of steps in any phase and the first step. A transfer bias having a voltage waveform in which the absolute value of the voltage is larger than the absolute value of the voltage after the second stage and the voltage application time at the first stage is shorter than the sum of the voltage application times after the second stage. Thus, the voltage application unit is controlled.

  According to the present invention, it is possible to realize high transferability to a concave portion of a sheet.

1 is a diagram schematically showing an overall configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a main part of a control system of the image forming apparatus in FIG. 1. FIG. 6 is a diagram illustrating a phenomenon in which white spots are locally generated in a concave portion of a sheet. It is a figure which shows the electric force line of the alternating current electric field in the recessed part of a paper. FIG. 5 is a diagram illustrating a relationship between electric lines of force and toner particle trajectories in a concave portion of a sheet. FIG. 2 is a diagram illustrating a secondary transfer bias from a voltage application unit of the image forming apparatus in FIG. 1. FIG. 7 is a diagram illustrating a first modification of the secondary transfer bias in FIG. 6. FIG. 7 is a diagram illustrating a second modification of the secondary transfer bias in FIG. 6. FIG. 7 is a diagram illustrating a third modification of the secondary transfer bias in FIG. 6.

Hereinafter, the present embodiment will be described in detail with reference to the drawings.
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 is a block diagram showing the 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. In other words, the image forming apparatus 1 transfers Y (yellow), M (magenta), C (cyan), and K (black) toner images formed on the photosensitive drum 413 to an intermediate transfer belt (first transfer member). The image is transferred (primary transfer) to 421, and the four color toner images are superimposed on the intermediate transfer belt 421, and then transferred (secondary transfer) to the paper S 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 storage unit 70, a communication unit 80, A voltage application unit 90 that applies a secondary transfer bias to the secondary transfer roller 424 and a control unit 100 are provided.

  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 70 are referred to. The storage unit 70 is configured by, 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 80. 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 80 is configured by a communication control card such as a LAN card, for example.

  As shown in FIG. 1, 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 a 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, an image status display, an operation status of each function, and the like in accordance with 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, 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 (eg, 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, for example, a two-component developing type developing device, and visualizes an electrostatic latent image by attaching toner of each color component (oilless toner containing wax in toner particles) to the surface of the photosensitive drum 413. Thus, a toner image is formed. 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 intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller 422, a plurality of support rollers 423, a secondary transfer roller (second transfer member) 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 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 (transfer nip) for transferring the toner image from the intermediate transfer belt 421 to the paper S. The

  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 secondary transfer bias having a rectangular wave AC voltage is applied to the secondary transfer roller 424, and the reverse polarity and the same polarity as the toner are applied to the back side of the paper S (the side in contact with the secondary transfer roller 424). The toner image is electrostatically transferred to the paper S by alternately applying the electric charges. The secondary transfer bias is generated by the voltage application unit 90 under the control of the control unit 100 and is applied from the voltage application unit 90 to the secondary transfer roller 424. The voltage waveform of the secondary transfer bias will be described later. The sheet S to which the toner image is transferred is conveyed toward the fixing unit 60.

  The belt cleaning unit 426 includes a belt cleaning blade that is in sliding contact with the surface of the intermediate transfer belt 421 and 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 (a so-called belt-type secondary transfer unit) in which an endless belt is stretched around a plurality of support rollers including the secondary transfer roller in a loop shape may be employed. .

  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 the fixing unit 60 performs a fixing process. 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.

  The overall configuration of the image forming apparatus 1 has been described above.

  By the way, when the paper S is rough paper, in the related art, there is a possibility that white spots are locally generated in the concave portion of the paper S. Specifically, as shown in FIG. 3, when an AC electric field is formed by applying a secondary transfer bias between the paper S, which is rough paper, and the intermediate transfer belt 421, the toner particles 500 are separated from the paper S according to the AC electric field. It reciprocates between the intermediate transfer belt 421. At that time, the toner particles 500 gradually behave toward the deepest portion of the concave portion every time they reciprocate. Finally, the toner particles 500 are aggregated at the deepest portion R1 of the concave portion (color density becomes higher than necessary in the fixed image), and the toner particles 500 disappear at the peripheral portion R2 in the concave portion (fixing). White spots in the image).

  The inventor has paid attention to the fact that the shape of the concave portion of the paper S can contribute to the above phenomenon. That is, in the recess shown in FIG. 3, the deepest portion R1 is a flat surface parallel to the surface of the intermediate transfer belt 421 during transfer, but the peripheral portion R2 is the surface of the intermediate transfer belt 421 during transfer. The inclined surface is not parallel to On the flat surface, since the paper thickness is uniform, the paper resistance with respect to the secondary transfer bias becomes uniform. As a result, the electric lines of force extending from the deepest portion R1 are straight along the direction of secondary transfer bias application as shown in FIG. It becomes a shape. The toner particles positioned on such a line of electric force that is linear in the vertical direction can reciprocate linearly in the vertical direction along the extending direction of the line of electric force. On the other hand, on the inclined surface, the paper resistance is non-uniform because the paper thickness is non-uniform. As a result, as shown by being surrounded by a broken line in FIG. 4, the electric lines of force extending from the peripheral portion R <b> 2 are swelled in a direction with a lower sheet resistance (in other words, a deeper recess or a thinner sheet S). Arc shape. For example, as shown in FIG. 5, when the toner particles 500 located in a region having such arc-shaped electric force lines in the electric field are separated from the intermediate transfer belt 421, the direction along the direction in which the electric force lines extend. However, since an inertial force (centrifugal force) corresponding to the mass acts on the toner particles 500, the toner particles 500 move along an arc-shaped electric force line (broken arrows in FIG. 5). I can't continue. The toner particles 500 move in the tangential direction of the arc-shaped electric force line (solid line arrow in FIG. 5), and the arrival point on the paper S is deeper (thinner) than the position of the end point of the electric force line. (Hereinafter, such behavior is referred to as “centrifugal scattering” in the sense of “scattering affected by centrifugal force”). When the toner particles 500 reciprocate in accordance with an alternating electric field, the toner particles 500 are gradually drawn to a deep (thin) place by centrifugal scattering each time the toner particles 500 reciprocate. As a result, as described above, the toner particles 500 aggregate at the deepest portion R1 of the concave portion, and white spots occur in the peripheral portion R2. In contrast to the phenomenon described above, in the present embodiment, centrifugal scattering is suppressed by adjusting the voltage waveform of the secondary transfer bias as will be described in detail below, and as a result, local white spots in the recesses of the paper S are suppressed. Plan.

  FIG. 6 is a diagram illustrating the secondary transfer bias output from the voltage application unit 90. The secondary transfer bias shown in FIG. 6 is a rectangular-wave AC voltage whose voltage value changes in two steps on each of the minus side and the plus side. Here, since the negative secondary transfer bias is the transfer voltage, the negative side is referred to as the transfer voltage side. Since the positive secondary transfer bias is a return voltage, the positive side is referred to as the return voltage side. The secondary transfer bias is applied to the secondary transfer roller 424, and the secondary transfer roller 424 is charged to a negative polarity by applying a transfer voltage and charged to a positive polarity by applying a return voltage. When the secondary transfer roller 424 is negatively charged, a force directed toward the sheet S side acts on the toner charged positively on the intermediate transfer belt 421. When the secondary transfer roller 424 is positively charged, a force directed toward the intermediate transfer belt 421 acts on the toner that is positively charged on the paper S.

  In both the voltage waveform of the phase on the transfer voltage side and the voltage waveform of the phase on the return voltage side, the voltage value of the first stage is higher than the voltage value of the second stage (that is, the absolute value is large), and the voltage of the first stage The application time is shorter than the voltage application time in the second stage. Specifically, in the phase on the transfer voltage side, the first-stage voltage Vn1 is higher than the second-stage voltage Vn2 (that is, | Vn1 |> | Vn2 |), and the first-stage voltage application time Tn1 is two-stage. It is shorter than the voltage application time Tn2 of the eye (that is, Tn1 <Tn2). Similarly, in the phase on the return voltage side, the first-stage voltage Vp1 is higher than the second-stage voltage Vp2 (that is, | Vp1 |> | Vp2 |), and the first-stage voltage application time Tp1 is the second-stage voltage. It is shorter than the application time Tp2 (that is, Tp1 <Tp2). Further, the total voltage application time Tn on the transfer voltage side (that is, Tn1 + Tn2) and the total voltage application time Tp on the return voltage side (that is, Tp1 + Tp2) are the same.

  The second-stage voltages Vn2 and Vp2 are preferably 10% or more and less than 50% of the first-stage voltages Vn1 and Vp1. In addition, it is desirable that the voltage application time of the first stage is 10% or more and less than 30% with respect to the voltage application time of the voltages Vn2 and Vp2 of the second stage. When the secondary transfer bias is a rectangular-wave AC voltage whose voltage value changes in three steps or more on each of the transfer voltage side and the return voltage side, the secondary transfer bias is 1 for the total voltage application time in the second and subsequent steps. It is desirable that the voltage application time of the stage is 10% or more and less than 30%, and that the voltage values after the second stage are all 10% or more and less than 50% of the voltage value of the first stage.

  FIG. 6 shows one cycle of the secondary transfer bias. During transfer, the secondary transfer bias in the drawing is repeatedly output from the voltage application unit 90 in order to generate an alternating electric field.

An example of the set value of the secondary transfer bias shown in FIG. 6 will be given.
Vn1 = -8kV, Vn2 = -2kV
Vp1 = 8kV, Vp2 = 2kV
Tn1: Tn2 = 2: 8
Tn1 = Tp1, Tn2 = Tp2, Tn = Tp
Voff (offset voltage) = 0 kV

  Next, a modified example of the secondary transfer bias will be described.

[Modification 1]
FIG. 7 is a diagram illustrating a first modification of the voltage waveform of the secondary transfer bias. As shown in the figure, the secondary transfer bias of Modification 1 is such that the waveforms on the transfer voltage side (minus side) and the return voltage side (plus side) are not targeted. In this example, the transfer voltage side has three stages and the return voltage side has two stages.

An example of the set value of the secondary transfer bias shown in FIG. 7 will be given.
Vn1 = -8 kV, Vn2 = -2 kV, Vn3 = -2 kV
Vp1 = 7kV, Vp2 = 1.5kV
Tn1: (Tn2 + Tn3) = 1.5: 8.5
Tp1: Tp2 = 2: 8
Tn: Tp = 6: 4 (relationship of Tn> Tp)
Voff (offset) = 0 kV

  In the first modification, the integration value on the transfer voltage side of the secondary transfer bias (in the figure, the hatched portion indicated by the one-dot chain line) is larger than the integral value on the return voltage side (the hatched portion indicated by the solid line in the drawing). Yes. Since the transferability is determined by the total voltage (that is, total energy) corresponding to the integral value, the transferability adjustment is performed by adjusting the integral value on the transfer voltage side with respect to the return voltage side integral value as in Modification 1. Can be achieved.

[Modification 2]
FIG. 8 is a diagram illustrating a second modification of the secondary transfer bias. As shown in the figure, the secondary transfer bias of Modification 2 has a non-target waveform on the transfer voltage side (minus side) and return voltage side (plus side), and has a negative offset voltage as a DC component. It is. In this example, the transfer voltage side has two steps, the return voltage side has three steps, and the offset voltage is −1V. It should be noted that it is necessary to prevent the return voltage side from becoming 0 V or less by giving a negative offset. That is, the absolute value of the offset voltage is made smaller than the absolute value of the minimum voltage of the AC component having a phase opposite to that of the offset voltage (that is, | Vp2 |> | Voff |).

An example of the set value of the secondary transfer bias shown in FIG. 8 will be given.
Vn1 = -6kV, Vn2 = -2kV
Vp1 = 8 kV, Vp2 = 1.5 kV, Vp3 = 2.5 kV
Tn1: Tn2 = 3: 7
Tp1: (Tp2 + Tp3) = 2.5: 7.5
Tn: Tp = 5: 5
Voff (offset) = -1 kV

[Modification 3]
FIG. 9 is a diagram illustrating a third modification of the secondary transfer bias. As shown in the figure, in the secondary transfer bias of Modification 3, the first-stage waveform on the plus / minus bipolar side of the secondary transfer bias of the embodiment shown in FIG. 9 is a trapezoidal wave instead of a rectangular wave. Is. Thus, the waveform is not limited to a rectangular wave, and may be any waveform, for example, a waveform obtained by synthesizing a sine wave, a triangular wave, or the like. When such a composite waveform is used, the end point of the first stage is defined as the time when the voltage value drops to 60% of the peak voltage value.

  As described above, according to the present embodiment, the voltage waveform of the secondary transfer bias (transfer bias) applied to the secondary transfer roller 424 is alternately set to the phase corresponding to the transfer voltage and the phase corresponding to the return voltage. In addition, in any waveform, the voltage value changes in a plurality of stages, and the absolute value of the voltage at the first stage is larger than the absolute value of the voltage at the second stage and the first stage. The voltage application time was made shorter than the voltage application time after the second stage. As a result, the voltage application time for forming a relatively strong electric field can be kept short, so that excessive reciprocation of the toner particles is suppressed, so that the centrifugal scattering of the toner particles is suppressed. Therefore, local white spots in the inclined portion and local high concentration in the flat portion can be suppressed. That is, regardless of the shape of the concave portion of the paper S, high transferability to the concave portion of the paper S can be realized.

  The above-described embodiment is merely an example of the implementation of the present invention, and the technical scope of the present invention should not be construed in a limited manner. That is, the scope of the present invention is shown not by the above description but by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

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 70 Memory | storage part 80 Communication part 90 Voltage application part 100 Control part 101 CPU
102 ROM
103 RAM
421 Intermediate transfer belt 424 Secondary transfer roller 500 Toner particle S Paper R1 Deepest part R2 Peripheral part

Claims (7)

A first transfer member carrying a toner image;
A second transfer member that forms a transfer nip with the first transfer member;
A voltage applying unit that applies a transfer bias having a voltage waveform including an AC component that alternately repeats a phase corresponding to the transfer voltage and a phase corresponding to the return voltage to the second transfer member;
With
The voltage waveform has a voltage value that changes in a plurality of stages in any phase, the absolute value of the voltage of the first stage is larger than the absolute value of the voltage after the second stage, and the voltage application time of the first stage is 2 Shorter than the total voltage application time after the stage,
Transfer device. The voltage application time of the first stage is 10% or more and less than 30% of the total voltage application time after the second stage.
The transfer device according to claim 1. The electric field intensity generated by the voltage application in the second stage and thereafter is 10% or more and less than 50% of the electric field intensity generated by the voltage application in the first stage.
The transfer apparatus according to claim 1 or 2. The voltage integral value of the phase corresponding to the transfer voltage is not less than the voltage integral value of the phase corresponding to the return voltage.
The transfer device according to any one of claims 1 to 3. The transfer bias further includes an offset voltage as a DC component, and the absolute value of the offset voltage is smaller than the absolute value of the minimum voltage of the AC component having a phase opposite to the offset voltage.
The transfer device according to any one of claims 1 to 4.   An image forming apparatus comprising the transfer device according to claim 1. A transfer control method for transferring a toner image to a sheet at a transfer nip by applying a transfer bias,
A control step of controlling a voltage application unit for applying the transfer bias,
The control step is a voltage waveform including an AC component that alternately repeats a phase corresponding to the transfer voltage and a phase corresponding to the return voltage, and the voltage value changes in a plurality of steps in any phase and the first step. A transfer bias having a voltage waveform in which the absolute value of the voltage is larger than the absolute value of the voltage after the second stage and the voltage application time at the first stage is shorter than the sum of the voltage application times after the second stage. So as to control the voltage application unit,
Transcription control method.

Images