Image forming apparatus, control method, and storage medium

Abstract

To provide an image forming apparatus capable of preventing an image to be formed from being affected by scattering of toner of a lowermost toner layer of a multilayer toner image to be transferred onto a recording medium.SOLUTION: An image forming apparatus that forms a toner image by superimposing toner layers on an intermediate transfer body and transfers the formed toner image onto a recording medium, the image forming apparatus comprising: a controller that performs specific control to make a volume of a lowermost toner layer of a multilayer toner image transferred onto the recording medium smaller than a volume of a single-layer toner image transferred onto the recording medium when the single-layer toner image is formed by a single-color toner layer, the multilayer toner image being formed by superimposing toner layers of a plurality of colors having the same pattern as the single-layer toner layer.SELECTED DRAWING: Figure 14

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus, a control method, and a control program. [Background technology]

[0002] In an electrophotographic image forming apparatus, for example, an electrostatic latent image formed by exposing a charged photosensitive member to light is developed with toner to form a toner image on the surface of the photosensitive member, the toner image is transferred to an intermediate transfer member, and then transferred from the intermediate transfer member to a recording medium. After that, a fixing process is performed in which the toner image on the recording medium is fixed by heating and pressurizing the toner image on the recording medium, thereby forming an image on the recording medium.

[0003] 2. Description of the Related Art When a toner image is formed on a recording medium, a phenomenon is known in which toner from the toner image scatters outside the area where the toner image is to be formed.

[0004] The following prior art is disclosed in Patent Document 1: The edge of an object constituting an image formed by sequentially transferring multiple colors of toner onto a recording medium is detected. At the edge, the area of ​​a first toner layer formed from one color of toner that is transferred first onto the recording medium is expanded by a specific pixel so that the area of ​​the first toner layer is larger than the area of ​​a second toner layer formed from a toner of another color that is transferred second or later. As a result, even if toner from the second toner layer scatters from above the toner in the first toner layer, the toner in the expanded portion of the first toner layer serves to catch the toner from the second toner layer, preventing the toner from scattering from the image. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-203298 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when forming an image such as a character or line image by overlaying a bottom layer of white toner with other color toners in the same pattern as the white toner, there is a possibility that the white toner may scatter outside the pattern. In this case, the white toner that has scattered outside the pattern may extend outside the pattern of the other color toners, resulting in an unintended image with a white border. This phenomenon is more noticeable when the image is formed on a transparent film or the like. The above prior art does not take into consideration the scattering of the bottom layer of toner, and therefore cannot address the above problem.

[0007] The present invention has been made to solve such problems, and aims to provide an image forming apparatus, a control method, and a control program that can prevent the scattering of toner from the bottom toner layer of a multi-layer toner image transferred onto a recording medium from affecting the formed image. [Means for solving the problem]

[0008] The above-mentioned problems of the present invention are solved by the following means.

[0009] (1) An image forming apparatus that forms a toner image by superimposing each toner layer on an intermediate transfer body and transfers the formed toner image onto a recording medium, the image forming apparatus having a control unit that performs specific control to make the volume of the toner layer of the same color as the monochromatic toner layer, which is the bottom layer of the multi-layer toner image transferred onto the recording medium when forming a multi-layer toner image by superimposing each toner layer of multiple colors in the same pattern as the monochromatic toner layer, smaller than the volume of the monochromatic toner image transferred onto the recording medium when forming a monochromatic toner image.

[0010] (2) An image forming apparatus as described in (1) above, which has an image signal generating unit that generates an image signal based on print data, and a toner image forming unit that forms the toner image based on the image signal, and the control unit performs the specific control by causing the image signal generating unit to generate the image signal in which the area of ​​the bottom toner layer of the multi-layer toner image to be transferred onto the recording medium is reduced by a predetermined number of pixels from the area of ​​the upper toner layer.

[0011] (3) An image forming apparatus as described in (1) above, comprising a photosensitive member, a charging unit that uniformly charges the photosensitive member, a writing unit that forms an electrostatic latent image on the photosensitive member using a laser, and a developing unit that develops the electrostatic latent image formed on the photosensitive member using toner, wherein the control unit performs the specific control by reducing the amount of light from the laser that forms the electrostatic latent image to form the bottom toner layer of the multi-layer toner image that is transferred onto the recording medium.

[0012] (4) An image forming apparatus as described in (1) above, comprising a photosensitive member, a charging unit that uniformly charges the photosensitive member, a writing unit that forms an electrostatic latent image on the photosensitive member using a laser, and a developing unit that develops the electrostatic latent image formed on the photosensitive member using toner, wherein the control unit performs the specific control by reducing the development voltage applied by the developing unit when developing the bottom toner layer of the multi-layer toner image transferred onto the recording medium.

[0013] (5) An image forming apparatus as described in (1) above, which has a primary transfer unit that contacts a photosensitive member via the intermediate transfer member and transfers the toner layer on the photosensitive member onto the intermediate transfer member, and the control unit performs the specific control by changing the primary transfer bias of the primary transfer unit when transferring the bottommost toner layer of the multi-layer toner image to be transferred onto the recording medium onto the intermediate transfer member.

[0014] (6) An image forming apparatus as described in (1) above, which has a secondary transfer unit that contacts the intermediate transfer body via the recording medium and transfers the toner image on the intermediate transfer body onto the recording medium, and the control unit performs the specific control by changing the secondary transfer bias of the secondary transfer unit when forming the multi-layer toner image on the recording medium.

[0015] (7) The image forming apparatus according to (1) above, wherein the control unit changes the amount of reduction in the volume of the bottommost toner layer of the multi-layer toner image in the specific control depending on the type of recording medium acquired.

[0016] (8) The image forming apparatus according to (1) above, wherein the particle size of the toner in the lowermost toner layer of the multi-layer toner image is 1 μm or more larger than the particle size of the toner in the upper toner layer.

[0017] (9) The image forming apparatus according to (1) above, wherein the circularity of the toner in the bottom toner layer of the multi-layer toner image is smaller than the circularity of the toner in the upper toner layer by 2% or more.

[0018] (10) The image forming apparatus according to (1) above, wherein the specific gravity of the toner in the lowermost toner layer of the multi-layer toner image is 1.3 times or more the specific gravity of the toner in the upper toner layer.

[0019] (11) The image forming apparatus according to (1) above, wherein the average Q / M of the toner in the lowermost toner layer of the multi-layer toner image is 0.8 times or less the average Q / M of the toner in the upper toner layer.

[0020] (12) The image forming apparatus according to (1) above, wherein the toner in the bottom toner layer of the multi-layer toner image is produced by a pulverization method, and the toner in the top toner layer is produced by a polymerization method.

[0021] (13) An image forming apparatus as described in (1) above, wherein the toner color of the toner layer other than the bottom layer of the multi-layer toner image is yellow, magenta, cyan, or black, and the toner of the bottom layer is a color other than yellow, magenta, cyan, and black.

[0022] (14) A control method for an image forming device that forms a toner image by superimposing each toner layer on an intermediate transfer body and transfers the formed toner image onto a recording medium, the control method comprising a step of making the volume of the bottommost toner layer of the same color as the monochromatic toner layer of the multi-layer toner image that is transferred onto the recording medium when forming a multi-layer toner image by superimposing each toner layer of multiple colors in the same pattern as the monochromatic toner layer smaller than the volume of the monochromatic toner image that is transferred onto the recording medium when forming a monochromatic toner image.

[0023] (15) A control program for an image forming device that forms a toner image by superimposing each toner layer on an intermediate transfer body and transfers the formed toner image onto a recording medium, the control program causing a computer to execute a step of making the volume of the bottommost toner layer of the same color as the monochromatic toner layer of the multilayer toner image transferred onto the recording medium when forming a multilayer toner image by superimposing each toner layer of multiple colors in the same pattern as the monochromatic toner layer smaller than the volume of the monochromatic toner image transferred onto the recording medium when forming a monochromatic toner image. [Effects of the Invention]

[0024] The volume of the bottommost toner layer of the same color as the single-color toner layer of a multi-layer toner image, in which toner layers of multiple colors having the same pattern as the single-color toner layer are superimposed, is made smaller than the volume of the toner image of the single-color toner layer transferred onto the recording medium, thereby preventing the scattering of toner from the bottommost toner layer of the multi-layer toner image transferred onto the recording medium from affecting the formed image. [Brief explanation of the drawings]

[0025] Advantages and features provided by one or more embodiments of the present invention will be more fully understood from the following detailed description and the accompanying drawings, which are for purposes of illustration only and are not intended to be limiting. [Figure 1] FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus. [Figure 2] FIG. 1 is a block diagram showing a configuration of an image forming apparatus. [Figure 3] FIG. 2 is an explanatory diagram showing a toner layer formed on each photosensitive drum. [Figure 4] FIG. 2 is a configuration diagram of a main part of an imaging unit. [Figure 5] 10 is a photograph of a comparative example in which a specific multi-layer toner image is formed on tack paper. [Figure 6] FIG. 10 is an explanatory diagram showing a state in which toner in the lowermost toner layer scatters during primary transfer. [Figure 7] FIG. 10 is an explanatory diagram showing a state in which toner in the lowermost toner layer scatters during secondary transfer. [Figure 8] 10A and 10B are explanatory diagrams showing the state of the toner layer of each color on each photosensitive drum before primary transfer, comparing a comparative example in which specific control is not performed with the present embodiment in which specific control is performed. [Figure 9] 10A and 10B are explanatory diagrams showing the state of the toner layer of each color on the film after secondary transfer, comparing a comparative example in which specific control is not performed with this embodiment in which specific control is performed. [Figure 10] 10A and 10B are explanatory diagrams showing multi-layer toner images other than the specific multi-layer toner image; [Figure 11] FIG. 4 is an explanatory diagram showing a specific multi-layer toner image. [Figure 12] FIG. 10 is a diagram showing a comparison between a photograph of a comparative example in which a specific multi-layer toner image is formed on tack paper without specific control and a photograph of an example in which a specific multi-layer toner image is formed by specific control. [Figure 13] FIG. 10 is a diagram showing a comparison between a photograph of a comparative example in which a specific multi-layer toner image is formed on foil paper without specific control and a photograph of an example in which a specific multi-layer toner image is formed with specific control. [Figure 14] FIG. 4 is a flowchart illustrating the operation of the image forming apparatus. [Figure 15] 10A and 10B are explanatory diagrams showing the state of the toner layer of each color on each photosensitive drum before primary transfer, comparing a comparative example in which specific control is not performed with the present embodiment in which specific control is performed. [Figure 16] 10A and 10B are explanatory diagrams showing the state of the toner layer of each color on the film after secondary transfer, comparing a comparative example in which specific control is not performed with this embodiment in which specific control is performed. [Figure 17] 10A and 10B are explanatory diagrams showing the state of the toner layer of each color on each photosensitive drum before primary transfer, comparing a comparative example in which specific control is not performed with the present embodiment in which specific control is performed. [Figure 18] 10A and 10B are explanatory diagrams showing the state of the toner layer of each color on the film after secondary transfer, comparing a comparative example in which specific control is not performed with this embodiment in which specific control is performed. DETAILED DESCRIPTION OF THE INVENTION

[0026] An image forming apparatus, a control method, and a control program according to an embodiment of the present invention will be described below with reference to the drawings. However, the scope of the present invention is not limited to the disclosed embodiments. In the drawings, identical elements are designated by the same reference numerals, and redundant explanations will be omitted. Furthermore, the dimensional proportions in the drawings are exaggerated for the sake of explanation and may differ from the actual proportions.

[0027] (First embodiment) Fig. 1 is a schematic diagram showing the configuration of an image forming apparatus 100. Fig. 2 is a block diagram showing the configuration of the image forming apparatus 100.

[0028] Image forming apparatus 100 includes control unit 110, storage unit 120, communication unit 130, operation display unit 140, image reading unit 150, image control unit 160, and image forming unit 170. These components are communicably connected to one another via bus 180. Image forming apparatus 100 may be configured as an MFP (Multi Function Peripheral). Control unit 110 and image control unit 160 constitute a control unit. Control unit 110, storage unit 120, operation display unit 140, and image control unit 160 constitute a computer.

[0029] The control unit 110 includes a CPU (Central Processing Unit) and various memories, and controls the above-mentioned units and performs various arithmetic processing according to a program. The operation of the control unit 110 will be described later.

[0030] The storage unit 120 is configured by a solid state drive (SDD) or a hard disk drive (HDD), and stores various programs and various data.

[0031] The communication unit 130 is an interface for communicating between the image forming apparatus 100 and an external device. A network interface conforming to standards such as Ethernet (registered trademark), SATA, or IEEE1394 is used as the communication unit 130. Alternatively, various local connection interfaces such as wireless communication interfaces such as Bluetooth (registered trademark) or IEEE802.11 are used as the communication unit 130.

[0032] The operation display unit 140 includes a touch panel, a numeric keypad, a start button, a stop button, and the like, and is used to display various information and input various instructions.

[0033] Image reading unit 150 has a light source such as a fluorescent lamp and an imaging element such as a CCD (Charge Coupled Device) image sensor. Image reading unit 150 irradiates a document set at a predetermined reading position with light from the light source, photoelectrically converts the reflected light with the imaging element, and generates image data from the electrical signal.

[0034] Image control unit 160 performs layout processing and rasterization processing on print data included in a print job or the like received by communication unit 130, and generates image data in bitmap format. The image data is output to image forming unit 170 as an image signal to be used for exposure by image forming unit 170, which will be described later. The image signal corresponds to the image data, and since the image data is generated based on the print data, it can be said that the image signal is generated based on the print data. Image control unit 160 constitutes an image signal generation unit.

[0035] A print job is a general term for a print command to image forming apparatus 100, and includes print data and print settings. Print data is document data to be printed, and may include various types of data, such as image data, vector data, and text data. Specifically, print data may be PDL (Page Description Language) data, PDF (Portable Document Format) data, or TIFF (Tagged Image File Format) data. Print settings are settings related to image formation on a recording medium, and may include various settings such as the number of pages, number of copies, type of recording medium, selection of color or monochrome, double-sided printing, and page layout.

[0036] The recording medium includes film, tack paper, foil paper, paper, containers, etc. For simplicity of explanation, the following description will be given taking the case where the recording medium is film 900 as an example.

[0037] Image forming unit 170 includes image creating unit 40, fixing unit 50, paper feeding unit 60, and paper transport unit 70. Paper transport unit 70 forms a transport path for transporting film 900 using a plurality of transport rollers 72. Image creating unit 40 forms a toner image forming unit.

[0038] The imaging unit 40 includes imaging units 41 (41Y, 41M, 41C, and 41K) corresponding to the toners of the respective colors of Y (yellow), M (magenta), C (cyan), and K (black). The imaging unit 40 may further include an imaging unit 41W corresponding to the toner of the special color W (white). Hereinafter, the imaging units 41 and the elements included in each imaging unit 41 will be denoted by the letters Y, M, C, K, and W only when distinguishing between the imaging units 41 and the elements included in each imaging unit 41. The imaging unit 41 includes a developing device 411, an optical writing unit 413, a charging unit 412, a photosensitive drum 414, and a primary transfer roller 415. The photosensitive drum 414 constitutes a photosensitive member. The developing device 411, the optical writing unit 413, the charging unit 412, and the photosensitive drum 414 may be provided as a replaceable set. Each imaging unit 41 forms a toner layer 500 on the photosensitive drum 414 through processes of charging, exposure, and development based on image data. The toner layer 500 formed on each photosensitive drum 414 is a pattern of toner 501 of a single color.

[0039] FIG. 3 is an explanatory diagram showing the toner layer 500 formed on each photosensitive drum 414.

[0040] In the example shown in FIG. 3, toner layers 500M, 500C, and 500W of three colors, M (magenta), C (cyan), and W (white), are formed on photosensitive drums 414M, 414C, and 414W, respectively.

[0041] The toner layers 500 formed on the photosensitive drums 414 are sequentially superimposed and primarily transferred onto the intermediate transfer belt 42 by electrostatic force due to a primary transfer voltage applied to the primary transfer rollers 415. As a result, color toner images 510 (see FIG. 6) are held on the intermediate transfer belt 42. The color toner images on the intermediate transfer belt 42 are secondarily transferred onto the film 900 by the secondary transfer rollers 43. The intermediate transfer belt 42 constitutes an intermediate transfer body.

[0042] The imaging unit 41 will now be described in more detail.

[0043] 4 is a configuration diagram of the main part of the image forming unit 41. In FIG.

[0044] The charging unit 412 applies a high voltage to the charging wire to generate a corona discharge, thereby charging the surface of the photosensitive drum 414. The charging potential of the photosensitive drum 414 is controlled by applying a voltage to the charging grid. The optical writing unit 413 performs exposure by forming an electrostatic latent image on the photosensitive drum 414 through scanning exposure using a laser diode. More specifically, the optical writing unit 413 performs exposure by driving the laser diode based on an image signal to form an electrostatic latent image on the photosensitive drum 414 through scanning exposure using the laser diode. The optical writing unit 413 constitutes a writing unit. The amount of laser light emitted during scanning exposure using the laser diode can be adjusted as follows each time the image forming apparatus 100 is started up: Halftone patches and solid patches are formed on the intermediate transfer belt 42, and the image density of each patch is detected by reading it using an IDC sensor. The amount of laser light is then adjusted so that the image densities of the halftone patches and solid patches each reach a predetermined image density.

[0045] In the developing device 411, a developer consisting of toner and magnetic carriers is held and transported on the surface of the developing sleeve 411A containing a magnetic substance. A developing voltage is applied to the developing sleeve 411A while the developing sleeve 411A is rotating, and the toner in the developer transported to the developing sleeve 411A is transferred to the latent image on the photosensitive drum 414, thereby developing the latent image into an image in the toner layer 500. The developing device 411 constitutes a developing unit. The developing voltage can be adjusted as follows each time the image forming apparatus 100 is started up: Halftone patches and solid patches are formed on the intermediate transfer belt 42, and the image density of each patch is detected by reading it with an IDC sensor. The developing voltage is then adjusted so that the image densities of the halftone patches and solid patches each reach a predetermined image density.

[0046] The photosensitive drum 414 of each image forming unit 41 is pressed against the primary transfer roller 415 via the intermediate transfer belt 42. This brings the photosensitive drum 414 into contact with the intermediate transfer belt 42. For example, by moving the primary transfer roller 415, the photosensitive drum 414 and the primary transfer roller 415 can be brought into contact with and separated from each other (contact and separation) via the intermediate transfer belt 42. A primary transfer bias is applied to the primary transfer roller 415. When the primary transfer bias is applied to the primary transfer roller 415 while the photosensitive drum 414 is in contact with the intermediate transfer belt 42, the toner image is transferred from the photosensitive drum 414 to the intermediate transfer belt 42 by electrostatic force from the primary transfer roller 415.

[0047] The photosensitive drum 414 is an image carrier having a hollow cylindrical main body (substrate) and a photosensitive layer, and is configured to rotate at a predetermined speed. The main body (substrate) is made of a metal such as aluminum. The photosensitive layer is made of a resin such as polycarbonate containing an organic photoconductor (OPC).

[0048] The intermediate transfer belt 42 has a volume resistivity of 1.0×10 7 ~1.0×10 9 Ω·cm, with a surface resistivity of 1.0×10 10 ~1.0×10 12 A semiconductive, endless (seamless) resin belt with a resistance of approximately Ω / □ is used. The resin belt may be a semiconductive resin film with a thickness of 0.05 to 0.5 mm, which is made of an engineering plastic, such as modified polyimide, thermosetting polyimide, ethylene tetrafluoroethylene copolymer, or polyvinylidene fluoride, with a conductive material dispersed therein. Alternatively, the intermediate transfer belt 42 may be a semiconductive rubber belt with a thickness of 0.5 to 2.0 mm, which is made of silicone rubber, urethane rubber, or the like, with a conductive material dispersed therein. The intermediate transfer belt 42 is wound around a plurality of roller members, including a tension roller 36, and is supported so as to be rotatable in the vertical direction.

[0049] The primary transfer rollers 415 are roller-shaped conductive members, for example, made of a metal shaft and foam rubber such as silicone or urethane covering the periphery. The primary transfer rollers 415 are disposed opposite the photosensitive drums 414 of each color, sandwiching the intermediate transfer belt 42 between them. They press against the back surface of the intermediate transfer belt 42 to form a transfer area between the primary transfer rollers 415 and the photosensitive drums 414. A primary transfer voltage of opposite polarity to that of the toner is applied to the primary transfer rollers 415 by constant voltage control. The electrostatic force of the transfer field formed in the transfer area causes the toner image on the photosensitive drum 414 to be primarily transferred onto the intermediate transfer belt 42. The primary transfer voltage is preset, for example, each time the image forming apparatus 100 is started up, so as to maximize the transfer efficiency of the toner layer of each color from the photosensitive drum 414 to the intermediate transfer belt 42. The primary transfer rollers 415 constitute a primary transfer unit. The primary transfer voltage constitutes a primary transfer bias.

[0050] The secondary transfer roller 43 is pressed against the intermediate transfer belt 42 via the film 900. This brings the secondary transfer roller 43 into contact with the intermediate transfer belt 42 via the film 900. A secondary transfer voltage is applied to the secondary transfer roller 43. When the secondary transfer voltage is applied to the secondary transfer roller 43 while the secondary transfer roller 43 is in contact with the intermediate transfer belt 42 via the film 900, the toner image is secondarily transferred from the intermediate transfer belt 42 to the film 900 by electrostatic force from the secondary transfer roller 43. The secondary transfer voltage is preset according to the type of recording medium, for example, each time the image forming apparatus 100 is started up, so as to optimize the transfer efficiency of the image transferred from the intermediate transfer belt 42 to a recording medium such as the film 900. Specifically, the secondary transfer voltage is preset to optimize the transfer efficiency, taking into consideration various types of toner images 510, such as a single-layer toner image 510 of a single color, a multi-layer toner image 510 of two or three colors, a solid toner image 510, and toner images 510 of various gradations. The secondary transfer roller 43 constitutes a secondary transfer unit. The secondary transfer voltage constitutes a secondary transfer bias.

[0051] Fixing unit 50 includes fixing roller 51a and pressure roller 52, and fixing roller 51a and pressure roller 52 are pressed against each other to form a nip between fixing roller 51a and pressure roller 52. Fixing unit 50 heats and pressurizes film 900 conveyed to the nip at the nip, and rotates fixing roller 51a and pressure roller 52, thereby heat-fixing toner image 510 on film 900 to the surface of film 900.

[0052] The film 900 on which the toner image 510 has been heat-fixed is discharged onto the paper discharge tray 90 by the transport rollers 72 .

[0053] If the print setting of the print job is double-sided printing, the paper transport unit 70 transports the film 900, on whose front surface the toner image 510 has been heat-fixed, to the ADU (Auto Duplex Unit) transport path 80. The film 900 transported to the ADU transport path 80 is turned over in a switchback path, and then merges with the transport path 71, where an image is formed again on the back side of the paper by the image forming unit 170.

[0054] The operation of the control unit 110 will now be described.

[0055] When the image forming unit 170 forms a multilayer toner image 510 by overlaying toner layers 500 of multiple colors with the same pattern, the control unit 110 performs specific control to reduce the volume of the bottom toner layer 500 of the multilayer toner image 510 transferred onto the film 900. Hereinafter, the bottom toner layer 500 of the multilayer toner image 510 will also be referred to simply as the “bottom toner layer.” The single-layer toner image 510 transferred onto the film 900 when forming the single-layer toner image 510 using single-color toner layers 500 will also be referred to simply as the “single-layer toner image.” The single toner layer 500 forming the single-layer toner image will also be referred to simply as the “single toner layer.” In the specific control, when the multilayer toner image 510 is formed by overlaying toner layers 500 of multiple colors with the same pattern as the single-layer toner image, the volume of the bottom toner layer of the same color as the single toner layer of the multilayer toner image 510 transferred onto the film 900 is reduced to be smaller than the volume of the single-layer toner image. When a multi-layer toner image 510 is formed by overlapping toner layers 500 of multiple colors having the same pattern, the multi-layer toner image 510 formed by overlapping toner layers 500 is also simply referred to as a "specific multi-layer toner image."

[0056] In this embodiment, specific control is performed by having the image control unit 160 generate an image signal in which the area of ​​the bottom toner layer of the specific multi-layer toner image transferred onto the film 900 is reduced by a predetermined number of pixels from the area of ​​the upper toner layer 500. Specifically, the image forming unit 170 reduces the area of ​​the bottom toner layer of the specific multi-layer toner image by a predetermined number of pixels from the area of ​​the upper toner layer 500 in the image data for each color obtained by rasterizing the print data. The image forming unit 170 then generates an image signal for image data in which the area of ​​the bottom toner layer of the specific multi-layer toner image is reduced by a predetermined number of pixels. In specific control, for example, the area of ​​the bottom toner layer can be reduced by a predetermined number of pixels by shifting the contour line of the pattern of the bottom toner layer inward relative to the pattern of the upper layer. The predetermined number of pixels can be set to an appropriate value through experiments, taking into account factors such as the effect of scattering of toner 501 on the image formed on the film 900 and changes in the color of the image formed on the film 900.

[0057] The specific control can prevent the scattering of toner 501 in the bottom toner layer from affecting the formed image. The mechanism by which the specific control prevents the scattering of toner 501 in the bottom toner layer from affecting the formed image will be described below.

[0058] (Impact on images due to scattering of toner in the bottom toner layer) Figure 5 is a photograph of a comparative example in which a specific multi-layer toner image is formed on tack paper. In the comparative example of Figure 5, tack paper with a transparent PP (polypropylene) surface substrate and a transparent PET (polyethylene terephthalate) release paper was used as the recording medium. The bottom-most toner image of the specific multi-layer toner image is formed with W (white) toner 501, and a toner layer 500 made of C (cyan) toner 501 in the same pattern as the bottom-most toner image is superimposed on top of the bottom-most toner image. Note that the photograph shown in Figure 5 was taken with black paper placed behind the tack paper.

[0059] 5, the W (white) toner 501 of the bottom toner image is scattered outside the pattern, causing the W (white) toner 501 to protrude from the pattern of the toner layer 500 made of the upper C (cyan) toner 501. This results in an image in which the pattern of the C (cyan) toner layer 500 is outlined in W (white).

[0060] (Mechanism causing toner scattering in the bottom toner layer) Fig. 6 is an explanatory diagram showing the state in which toner 501 of the lowermost toner layer scatters during primary transfer. Fig. 7 is an explanatory diagram showing the state in which toner 501 of the lowermost toner layer scatters during secondary transfer.

[0061] As shown in FIG. 6, there is a possibility that toner 501 in the bottom toner layer may scatter during primary transfer. This is thought to be because the adhesive force between the toner particles 501 in the bottom toner layer is relatively weak due to electrostatic force from primary transfer roller 415, so the edges are attracted to each other. The scattered toner 501 adheres to the intermediate transfer belt 42 outside the pattern of the toner layer 500. As a result, the scattered toner 501 is secondarily transferred to film 900 together with the specific multi-layer toner image, thereby affecting the image formed on film 900.

[0062] As shown in FIG. 7, there is a possibility that the toner 501 in the bottom toner layer may scatter during the secondary transfer. This is thought to be due to the following reason. During the secondary transfer, just before the specific multi-layer toner image is transported to the nip formed between the intermediate transfer belt 42 and the film 900, the toner 501 in the bottom toner layer on the intermediate transfer belt 42 is attracted by electrostatic force from the secondary transfer roller 43. The toner 501 in the bottom toner layer is prone to scattering because the adhesive force between the toner 501 particles is relatively weak, and the edge portions adhere to the film 900 outside the pattern. The scattered toner 501 adheres to the film 900 and is transported together with the film 900, and the specific multi-layer toner image on the intermediate transfer belt 42 is transported by the rotation of the intermediate transfer belt 42. As a result, the scattered toner 501 The toner image is secondarily transferred to the film 900 together with the specific multi-layer toner image in the nip formed between the intermediate transfer belt 42 and the film 900, thereby affecting the image formed on the film 900.

[0063] (Mechanism by which specific control prevents the scattering of toner from the bottom toner layer from affecting the image) 8 is an explanatory diagram showing a comparison of the state of the toner layer 500 of each color on each photosensitive drum 414 before the primary transfer between a comparative example in which the specific control is not performed and this embodiment in which the specific control is performed. FIG. 9 is an explanatory diagram showing a comparison of the state of the toner layer 500 of each color on the film 900 after the secondary transfer between a comparative example in which the specific control is not performed and this embodiment in which the specific control is performed.

[0064] 8, in this embodiment, specific control is performed by exposing the area of ​​the bottom toner layer of the specific multi-layer toner image transferred onto film 900 to an image signal that is reduced by a predetermined number of pixels from the area of ​​the upper toner layers. As a result, after development, the area of ​​W (white) toner layer 500W, which is the bottom toner layer, on photoconductor drum 414W becomes smaller than the areas of M (magenta) and C (cyan) toner layers, which are the upper layers, on photoconductor drum 414.

[0065] 9, in this embodiment, the area of ​​the W (white) toner layer 500W, which is the lowest toner layer, on the photosensitive drum 414W is reduced. Therefore, even if the lowest toner layer scatters outside the pattern of the lowest toner layer, it can be prevented from scattering outside the pattern of the upper toner layer 500. On the other hand, in the comparative example in which specific control is not performed, scattering of the lowest toner layer outside the pattern of the lowest toner layer can cause scattering outside the pattern of the upper toner layer 500.

[0066] Therefore, by using specific control, it is possible to prevent the scattering of toner from the bottom toner layer from affecting the image formed on the film 900.

[0067] As described above, in this embodiment, when a specific multi-layer toner image is formed, the area of ​​the bottom toner layer of the specific multi-layer toner image transferred onto the film 900 is reduced. On the other hand, when a multi-layer toner image other than the specific multi-layer toner image is formed, the specific control is not performed.

[0068] Fig. 10 is an explanatory diagram showing a multi-layer toner image other than the specific multi-layer toner image. Fig. 11 is an explanatory diagram showing the specific multi-layer toner image. Figs. 10 and 11 respectively show a multi-layer toner image other than the specific multi-layer toner image and a specific multi-layer toner image formed on film 900. Note that for the sake of convenience in explaining the difference between the specific multi-layer toner image and the multi-layer toner image other than the specific multi-layer toner image, the specific multi-layer toner image shown in Fig. 11 is the specific multi-layer toner image formed on film 900 when specific control is not performed.

[0069] The multi-layer toner image 510 other than the specific multi-layer toner image is a multi-layer toner image 510 in which the toner layers 500 of each color do not have the same pattern. Figure 10 shows a multi-layer toner image 510 in which only the pattern of the W (white) toner layer 500W, which is the bottom toner image, is larger in area than the C (cyan) and M (magenta) toner layers 500, which are the upper toner layers 500. The multi-layer toner image 510 shown in Figure 10 is included in the multi-layer toner images other than the specific multi-layer toner image. The multi-layer toner image 510 other than the specific multi-layer toner image includes, for example, a multi-layer toner image 510 for forming a black barcode image on a white background.

[0070] The specific multi-layer toner image is a multi-layer toner image 510 in which the toner layers 500 of each color have the same pattern. Figure 11 shows a specific multi-layer toner image in which the bottom toner image W (white) and the top toner layers 500 C (cyan) and M (magenta) have the same pattern.

[0071] The reason why specific control is not performed when forming multi-layer toner images 510 other than the specific multi-layer toner image is as follows: For example, when forming an image of a black barcode on a white background, even if toner layer 500W of W (white) that forms the white background scatters, the size of the white background only increases slightly, and the effect of the scattering of toner layer 500W is almost unnoticeable. By not performing specific control when forming multi-layer toner images 510 other than the specific multi-layer toner image, the amount of calculation by control unit 110 and image control unit 160 can be reduced.

[0072] (Relationship between the type of recording medium and the amount of reduction in the area of ​​the bottom toner layer of a specific multi-layer toner image transferred to the recording medium through specific control) 1. When the recording medium is a film such as PP or PET When the recording medium is a film 900 such as PP or PET, the amount of reduction in the area of ​​the bottom toner layer of the specific multi-layer toner image transferred to the recording medium can be relatively large. This is because film 900 has high electrical resistance and is easily charged, so toner 501 of the bottom toner layer is likely to scatter on the recording medium just before the nip where secondary transfer occurs. When the recording medium is a film such as PP or PET, the area of ​​the bottom toner layer of the specific multi-layer toner image transferred to the recording medium is reduced by 7 dots of pixels, for example, when the pixel density is 1200 dpi.

[0073] 2. When the recording medium is plain paper or coated paper When the recording medium is plain paper or coated paper, the amount of reduction in the area of ​​the bottom toner layer of the specific multi-layer toner image transferred to the recording medium can be relatively small. This is because plain paper and coated paper have low electrical resistance and are difficult to charge, so toner 501 of the bottom toner layer is less likely to scatter on the recording medium just before the nip where secondary transfer occurs. When the recording medium is plain paper or coated paper, the area of ​​the bottom toner layer of the specific multi-layer toner image transferred to the recording medium is reduced by, for example, 3 dots of pixels when the pixel density is 1200 dpi.

[0074] Figure 12 is a comparison between a photograph of a comparative example in which a specific multi-layer toner image is formed on tack paper without specific control and a photograph of an example in which a specific multi-layer toner image is formed with specific control.

[0075] In the example shown in Figure 12, tack paper was used, with a surface substrate made of transparent PP and a release paper made of transparent PET. The bottom toner image of the specific multi-layer toner image was formed with W (white) toner, and a toner layer 500 made of C (cyan) toner with the same pattern as the bottom toner image was superimposed on top of the bottom toner image. In the print data used in common in the example and comparative example, the patterns of the bottom toner image and the top toner layer 500 were straight line patterns with a line width of 0.5 mm. In the example, as a result of specific control, an image was formed on the tack paper using image data in which the line width of the bottom toner image was reduced by 0.14 mm.

[0076] 12, in the comparative example, the scattering of toner in the bottom toner layer resulted in an image in which the C (cyan) pattern in the upper layer was outlined with scattered W (white). In the example, the effect on the image caused by the scattering of toner in the bottom toner layer, as seen in the comparative example, was suppressed.

[0077] Figure 13 is a diagram comparing a photograph of a comparative example in which a specific multi-layer toner image is formed on foil paper without specific control, and a photograph of an example in which a specific multi-layer toner image is formed with specific control.

[0078] In the example shown in Figure 13, foil paper with a silver-coated surface was used. The bottom toner image of the specific multi-layer toner image was formed with W (white) toner, and a toner layer 500 made of C (cyan) toner with the same pattern as the bottom toner image was superimposed on top of the bottom toner image. In the print data commonly used in the example and comparative example, the patterns of the bottom toner image and the top toner layer 500 were straight line patterns with a line width of 0.5 mm. In the example, as a result of specific control, an image was formed on the foil paper using image data in which the line width of the bottom toner image was reduced by 0.06 mm.

[0079] 13, in the comparative example, the scattering of toner in the bottom toner layer results in an image in which the C (cyan) pattern in the upper layer is outlined with scattered W (white). In the example, the effect on the image caused by scattering of toner in the bottom toner layer, as seen in the comparative example, is suppressed.

[0080] The control unit 110 can change the amount of volume reduction of the bottom toner layer of the specific multi-layer toner image in specific control depending on the type of recording medium on which the image is formed. The control unit 110 can acquire the type of recording medium on which the image is formed by reading the print settings of the print data. The control unit 110 can also acquire the type of recording medium on which the image is formed from detection results from a media sensor. The control unit 110 can also acquire the type of recording medium on which the image is formed as setting information input to the operation and display unit 140. When the recording medium is film 900, the control unit 110 reduces the area of ​​the bottom toner layer of the specific multi-layer toner image transferred to the recording medium by, for example, 7 dots of pixels. When the recording medium is plain paper or coated paper, the control unit 110 reduces the area of ​​the bottom toner layer of the specific multi-layer toner image transferred to the recording medium by, for example, 3 dots of pixels. These reduction amounts can be associated with the type of recording medium and stored in advance in the storage unit 120. Regardless of the type of recording medium, the number of pixels to be reduced can also be directly input to the operation and display unit 140.

[0081] (Characteristics of the bottom toner layer of a specific multi-layer toner image) 1. Particle size of the toner in the bottom toner layer of a specific multi-layer toner image When the particle size of the toner in the bottom toner layer of the specific multi-layer toner image is 1 μm or more larger than the particle size of the toner in the upper toner layers, the specific control effectively prevents the scattering of the toner in the bottom toner layer from affecting the formed image. This is for the following reason: Toner with a relatively large particle size has a small adhesion area per unit volume, and therefore the adhesion between toner particles is weaker. Therefore, during the primary transfer, when the bottom toner layer is transferred onto the intermediate transfer belt 42 in a superimposed state with other toner layers, the toner in the bottom toner layer is likely to scatter onto the intermediate transfer belt 42. Furthermore, during the secondary transfer, when the specific multi-layer toner image is transferred onto the film 900, the toner in the bottom toner layer is likely to scatter onto the film 900 just before the specific multi-layer toner image is transported to the nip formed between the intermediate transfer belt 42 and the film 900.

[0082] 2. Circularity of the toner in the bottom toner layer of a specific multi-layer toner image When the circularity of the toner in the bottom toner layer of the specific multi-layer toner image is 2% or more lower than the circularity of the toner in the upper toner layers, the specific control effectively prevents the scattering of toner in the bottom toner layer from affecting the formed image. This is for the following reason: Toner with a relatively low circularity also has weaker adhesion between toner particles. Therefore, during the primary transfer, when the bottom toner layer is transferred onto the intermediate transfer belt 42 in a superimposed state with other toner layers, the toner 501 in the bottom toner layer is likely to scatter onto the intermediate transfer belt 42. Furthermore, during the secondary transfer, when the specific multi-layer toner image is transferred onto the film 900, the toner 501 in the bottom toner layer is likely to scatter onto the film 900 just before the specific multi-layer toner image is transported to the nip formed between the intermediate transfer belt 42 and the film 900.

[0083] 3. Specific gravity of the toner in the bottom toner layer of a specific multi-layer toner image When the specific gravity of the toner 501 in the bottom toner layer of a specific multi-layer toner image is 1.3 times or more the specific gravity of the toner 501 in the upper toner layers, the specific control effectively prevents the scattering of the toner in the bottom toner layer from affecting the formed image. This is for the following reason: Toner with a relatively high specific gravity has a small charge per unit weight. The toner 501 in the bottom toner layer is restrained to the intermediate transfer belt 42 by the transfer charge while overlapping with the toner 501 in the other toner layers 500 on the intermediate transfer belt 42. However, since the toner 501 with a relatively high specific gravity has a small charge, the restraining force is weaker. For this reason, when the bottom toner layer is transferred onto the other toner layers on the intermediate transfer belt 42 during the primary transfer, the toner 501 in the bottom toner layer is more likely to scatter onto the intermediate transfer belt 42. Also, during the secondary transfer, when the specific multi-layer toner image is transferred onto the film 900, the toner 501 of the bottom toner layer is likely to scatter onto the film 900 just before the specific multi-layer toner image is transported to the nip formed between the intermediate transfer belt 42 and the film 900.

[0084] 4. Q / M of the toner in the bottom toner layer of a specific multi-layer toner image When the average Q / M of the toner in the bottom toner layer of a specific multi-layer toner image is 0.8 times or less the Q / M of the toner in the upper toner layers, the specific control effectively prevents the scattering of the toner 501 in the bottom toner layer from affecting the formed image. Q / M is the ratio of charge to mass. This is for the following reason: Toner 501 with a relatively small Q / M has a small charge per unit mass. The toner 501 in the bottom toner layer is restrained to the intermediate transfer belt 42 by the transfer charge while overlapping with the toner 501 in other toner layers 500 on the intermediate transfer belt 42. However, since the toner 501 with a relatively small Q / M has a small charge, the restraining force is weaker. Therefore, during the primary transfer, when the bottom toner layer is transferred onto the intermediate transfer belt 42 in an overlapping state with the other toner layers, the toner 501 in the bottom toner layer is more likely to scatter onto the intermediate transfer belt 42. Also, during the secondary transfer, when the specific multi-layer toner image is transferred onto the film 900, the toner 501 of the bottom toner layer is likely to scatter onto the film 900 just before the specific multi-layer toner image is transported to the nip formed between the intermediate transfer belt 42 and the film 900.

[0085] 5. Characteristics of the bottom toner layer of a specific multi-layer toner image due to the manufacturing method of the toner When the toner of the bottom toner layer of a specific multi-layer toner image is produced by a pulverization method and the toner of the upper toner layers is produced by a polymerization method, the specific control effectively prevents the scattering of the toner 501 of the bottom toner layer from affecting the formed image. This is for the following reason: The toner 501 produced by a pulverization method has a low circularity. Toner 501 with a relatively low circularity also has a weak adhesive force between toner particles 501. For this reason, when the bottom toner layer is transferred onto the intermediate transfer belt 42 in a superimposed state with other toner layers 500 during the primary transfer, the toner 501 of the bottom toner layer is likely to scatter onto the intermediate transfer belt 42. Furthermore, when the specific multi-layer toner image is transferred onto the film 900 during the secondary transfer, the toner 501 of the bottom toner layer is likely to scatter onto the film 900 immediately before the specific multi-layer toner image is transported to the nip formed between the intermediate transfer belt 42 and the film 900.

[0086] 6. Color of the toner in the bottom layer of a specific multi-layer toner image When the toner in the bottom toner layer of a specific multi-layer toner image is a toner of a special color other than Y (yellow), M (magenta), C (cyan), and K (black), the specific control has a significant effect of preventing the scattering of toner in the bottom toner layer from affecting the formed image. This is for the following reason: Toner of a special color such as W (white) is required to have different properties, such as light-blocking properties, from the toners of Y (yellow), M (magenta), C (cyan), and K (black). For this reason, the physical properties of the toner 501 in the bottom toner layer often have the properties described in 1 to 5 above.

[0087] 14 is a flowchart showing the operation of image forming apparatus 100. This flowchart can be executed by control unit 110 in accordance with a program.

[0088] The control unit 110 determines whether print data has been acquired (S101). If the control unit 110 determines that print data has not been acquired (S101: NO), it executes step S101 again.

[0089] When control unit 110 determines that print data has been acquired (S101: YES), it determines whether or not a specific multi-layer toner image is included in toner image 510 formed on film 900 based on the print data (S102). When control unit 110 determines that a specific multi-layer toner image is not included in toner image 510 formed on film 900 based on the print data (S102: NO), it does not perform specific control.

[0090] When the control unit 110 determines that the toner image 510 formed on the film 900 based on the print data contains a specific multi-layer toner image (S102: YES), it executes specific control to reduce the area of ​​the bottom toner layer of the specific multi-layer toner image (S103).

[0091] (Second embodiment) A second embodiment will now be described. The present embodiment differs from the first embodiment in the following respects. In the first embodiment, specific control is performed by having the image control unit 160 generate an image signal in which the area of ​​the bottom toner layer of the specific multi-layer toner image to be transferred onto the film 900 is reduced by a predetermined number of pixels from the area of ​​the upper toner layer 500. On the other hand, in this embodiment, specific control is performed by reducing the amount of laser light from the optical writing unit 413, which forms an electrostatic latent image for forming the bottom toner layer of the specific multi-layer toner image to be transferred onto the film 900. In other respects, this embodiment is similar to the first embodiment, so duplicated explanations will be omitted or simplified.

[0092] 15 is an explanatory diagram showing a comparison of the state of the toner layer 500 of each color on each photosensitive drum 414 before primary transfer between a comparative example in which specific control is not performed and this embodiment in which specific control is performed. FIG. 16 is an explanatory diagram showing a comparison of the state of the toner layer 500 of each color on the film 900 after secondary transfer between a comparative example in which specific control is not performed and this embodiment in which specific control is performed.

[0093] As shown in FIG. 15 , in this embodiment, the control unit 110 performs specific control by reducing the laser light intensity of the optical writing unit 413, which forms an electrostatic latent image for forming the bottom toner layer of the specific multi-layer toner image to be transferred onto the film 900. The laser light intensity is reduced, for example, to 70 to 50% of the laser light intensity set at the time of startup of the image forming apparatus 100. As a result, after development, the volume of the W (white) toner layer 500W, which is the bottom toner layer, on the photosensitive drum 414W is smaller than the volume of the single-layer toner image transferred onto the film 900 when a single-layer toner image having the same pattern as the bottom toner layer is formed. This specific control reduces the height of the W (white) toner layer 500W, which is the bottom toner layer, after development, for example.

[0094] In this embodiment, the volume of the W (white) toner layer 500W, which is the lowest toner layer, on the photosensitive drum 414W is reduced. Therefore, as shown in FIG. 16, the amount of the lowest toner layer that scatters outside the pattern of the lowest toner layer during the primary transfer and secondary transfer can be reduced. On the other hand, in the comparative example in which specific control is not performed, the lowest toner layer scatters outside the pattern of the lowest toner layer, and thus may scatter outside the pattern of the upper toner layer 500.

[0095] Therefore, by using specific control, it is possible to prevent the scattering of toner from the bottom toner layer from affecting the image formed on the film 900.

[0096] (Third embodiment) A third embodiment will now be described. The present embodiment differs from the first embodiment in the following respects. In the first embodiment, specific control is performed by having the image control unit 160 generate an image signal in which the area of ​​the bottom toner layer of the specific multi-layer toner image to be transferred onto the film 900 is reduced by a predetermined number of pixels from the area of ​​the upper toner layer 500. On the other hand, in this embodiment, specific control is performed by reducing the development voltage of the developer 411 when developing the bottom toner layer of the specific multi-layer toner image to be transferred onto the film 900. In other respects, this embodiment is similar to the first embodiment, so duplicated explanations will be omitted or simplified.

[0097] 17 is an explanatory diagram showing a comparison of the state of the toner layer 500 of each color on each photosensitive drum 414 before primary transfer between a comparative example in which specific control is not performed and this embodiment in which specific control is performed. FIG. 18 is an explanatory diagram showing a comparison of the state of the toner layer 500 of each color on the film 900 after secondary transfer between a comparative example in which specific control is not performed and this embodiment in which specific control is performed.

[0098] As shown in FIG. 17, in this embodiment, the control unit 110 performs specific control by reducing the development voltage of the developer 411 when developing the bottom toner layer of the specific multi-layer toner image transferred onto the film 900. The development voltage is reduced, for example, to 70 to 50% of the development voltage set at the start-up of the image forming apparatus 100. As a result, after development, the volume of the bottom toner layer W (white) 500W on the photosensitive drum 414W becomes smaller than the volume of the single-layer toner image transferred onto the film 900 when a single-layer toner image having the same pattern as the bottom toner layer is formed. This specific control reduces the height of the bottom toner layer W (white) 500W after development, for example.

[0099] In this embodiment, the volume of the W (white) toner layer 500W, which is the lowest toner layer, on the photosensitive drum 414W is reduced. Therefore, as shown in FIG. 18, the amount of the lowest toner layer that scatters outside the pattern of the lowest toner layer during the primary transfer and secondary transfer can be reduced. On the other hand, in the comparative example in which specific control is not performed, the lowest toner layer scatters outside the pattern of the lowest toner layer, and thus may scatter outside the pattern of the upper toner layer 500.

[0100] Therefore, by using specific control, it is possible to prevent the scattering of toner from the bottom toner layer from affecting the image formed on the film 900.

[0101] (Fourth embodiment) A fourth embodiment will now be described. The present embodiment differs from the first embodiment in the following respects. In the first embodiment, specific control is performed by having the image control unit 160 generate an image signal in which the area of ​​the bottom toner layer of the specific multi-layer toner image to be transferred onto the film 900 is reduced by a predetermined number of pixels from the area of ​​the upper toner layer 500. On the other hand, in this embodiment, specific control is performed by changing the primary transfer voltage of the primary transfer roller 415 when transferring the specific multi-layer toner image to be transferred onto the film 900 onto the intermediate transfer belt 42. In other respects, this embodiment is similar to the first embodiment, and therefore, repeated explanations will be omitted or simplified.

[0102] The control unit 110 performs specific control by changing the primary transfer voltage of the primary transfer roller 415 when transferring the specific multi-layer toner image to be transferred onto the film 900 onto the intermediate transfer belt 42. In the specific control, the control unit 110 changes the value of the primary transfer voltage from the value of the primary transfer voltage that was set in advance when the image forming apparatus 100 was started up, etc.

[0103] In the specific control, whether to increase or decrease the primary transfer voltage can be appropriately set depending on the properties of the toner in the W (white) toner layer, which is the bottom toner layer. If the particle size of the bottom toner layer is relatively large and the bonding strength between the toner particles is relatively weak, reducing the primary transfer voltage weakens the electrostatic force attracting the toner in the bottom toner layer to the intermediate transfer belt 42, and the toner tends to be less likely to scatter. Therefore, in this case, specific control to decrease the primary transfer voltage can be performed. If the Q / M of the toner is small, increasing the primary transfer voltage may strengthen the binding force of the toner in the bottom toner layer on the intermediate transfer belt 42, and the toner may be less likely to scatter. Therefore, in this case, specific control to increase the primary transfer voltage can be performed. In the specific control, the primary transfer voltage may be changed by ±30% from a preset value.

[0104] (Fifth embodiment) A fifth embodiment will now be described. The present embodiment differs from the first embodiment in the following respects. In the first embodiment, specific control is performed by having the image control unit 160 generate an image signal in which the area of ​​the bottom toner layer of the specific multi-layer toner image to be transferred onto the film 900 is reduced by a predetermined number of pixels from the area of ​​the upper toner layer 500. On the other hand, in this embodiment, specific control is performed by changing the secondary transfer voltage of the secondary transfer roller 43 when transferring the specific multi-layer toner image to be transferred onto the film 900 from the intermediate transfer belt 42 to the film 900. In other respects, this embodiment is similar to the first embodiment, and therefore, repeated explanations will be omitted or simplified.

[0105] The control unit 110 performs specific control by changing the secondary transfer voltage of the secondary transfer roller 43 when transferring the specific multi-layer toner image to be transferred onto the film 900 from the intermediate transfer belt 42 onto the film 900. In the specific control, the control unit 110 changes the value of the secondary transfer voltage from the value of the secondary transfer voltage that is set in advance when the image forming apparatus 100 is started up, etc.

[0106] Whether to increase or decrease the secondary transfer voltage in the specific control can be appropriately determined through experiments based on the relationship between the secondary transfer voltage and the degree of toner scattering in the W (white) toner layer, which is the lowest toner layer. For example, decreasing the secondary transfer voltage weakens the electric field in front of the nip formed between the intermediate transfer belt 42 and the film 900 during secondary transfer, relative to the conveyance direction of the film 900. This weakens the force of the electric field attracting the toner 501 in the W (white) toner layer, which is the lowest toner layer, from the intermediate transfer belt 42, making the toner 501 less likely to scatter. However, if the secondary transfer voltage is too low, the binding force of the toner 501 by the film 900 after passing through the nip will weaken, and the toner may scatter on the film 900 after passing through the nip. For example, if the film 900 is made of PP and has a thickness of 100 μm, the secondary transfer voltage in the specific control may be varied by ±20% from a preset value.

[0107] (Relationship between specific multi-layer toner image pattern and specific control in the first to fifth embodiments) 1. When the pattern of a specific multi-layer toner image is a thin line or thin character In this case, it is preferable to perform the specific control of the second to fifth embodiments, because if the specific control of the first embodiment is performed in this case, the W (white) toner layer, which is the bottom toner layer, may disappear due to the specific control.

[0108] 2. When the specific multi-layer toner image pattern is large, or when the specific multi-layer toner image pattern is thick lines or thick characters In this case, it is preferable to perform the specific control of the first embodiment. This is because performing the specific control of the second to fourth embodiments in this case may have the following effects on the formed image: The amount of toner 501 in the W (white) toner layer, which is the lowest toner layer, adhering to the film 900 may decrease, reducing the concealment rate of the toner 501 and changing the color of the specific multi-layer toner image. Furthermore, performing the specific control of the fifth embodiment may reduce the secondary transfer voltage, thereby worsening the transferability from the intermediate transfer belt 42 to the film 900 and reducing the image density of the specific multi-layer toner image.

[0109] The embodiment provides the following advantages.

[0110] The volume of the bottommost toner layer of the same color as the single-color toner layer of a multi-layer toner image, in which toner layers of multiple colors having the same pattern as the single-color toner layer are superimposed, is controlled to be smaller than the volume of the toner image of the single-color toner layer transferred onto the recording medium, thereby preventing the scattering of toner from the bottommost toner layer of the multi-layer toner image transferred onto the recording medium from affecting the formed image.

[0111] In addition, an image signal is generated in which the area of ​​the bottom toner layer of the multi-layer toner image to be transferred onto the recording medium is reduced by a predetermined number of pixels from the area of ​​the top toner layer, and a toner image is formed based on the generated image signal. This makes it possible to simply and effectively prevent the scattering of toner from the bottom toner layer of the multi-layer toner image to be transferred onto the recording medium from affecting the formed image.

[0112] In addition, specific control is performed by reducing the amount of light from the laser that forms the electrostatic latent image for forming the bottom toner layer of the multi-layer toner image to be transferred onto the recording medium, thereby simply and effectively preventing the scattering of toner from the bottom toner layer of the multi-layer toner image to be transferred onto the recording medium from affecting the formed image.

[0113] In addition, specific control is performed by reducing the development voltage when developing the bottom toner layer of a multi-layer toner image transferred onto a recording medium, which makes it possible to simply and effectively prevent the scattering of toner from the bottom toner layer of the multi-layer toner image transferred onto a recording medium from affecting the formed image.

[0114] In addition, specific control is performed by changing the primary transfer bias when transferring the bottom toner layer of the multi-layer toner image onto the recording medium onto the intermediate transfer body, which makes it possible to simply and effectively prevent the scattering of toner from the bottom toner layer of the multi-layer toner image transferred onto the recording medium from affecting the formed image.

[0115] Furthermore, when forming a multi-layer toner image on a recording medium, specific control is performed by changing the secondary transfer bias of the secondary transfer unit, which makes it possible to simply and effectively prevent the scattering of toner from the bottom toner layer of the multi-layer toner image transferred onto the recording medium from affecting the formed image.

[0116] In addition, the amount of volume reduction of the bottom toner layer of the multi-layer toner image during specific control is changed depending on the type of recording medium acquired, which makes it possible to simply and effectively prevent the scattering of toner from the bottom toner layer of the multi-layer toner image transferred onto the recording medium from affecting the formed image.

[0117] Furthermore, specific control is performed when the particle size of the toner in the bottom toner layer of a multi-layer toner image is 1 μm or more larger than the particle size of the toner in the top toner layer, thereby improving the effect of specific control in preventing the scattering of toner in the bottom toner layer of a multi-layer toner image transferred onto a recording medium from affecting the formed image.

[0118] Furthermore, specific control is performed when the circularity of the toner in the bottom toner layer of a multi-layer toner image is 2% or more lower than the circularity of the toner in the top toner layer, thereby improving the effect of specific control in preventing the scattering of toner in the bottom toner layer of a multi-layer toner image transferred onto a recording medium from affecting the formed image.

[0119] Furthermore, specific control is performed when the specific gravity of the toner in the bottom toner layer of a multi-layer toner image is 1.3 times or more higher than the specific gravity of the toner in the top toner layer, thereby improving the effect of specific control in preventing the scattering of toner in the bottom toner layer of a multi-layer toner image transferred onto a recording medium from affecting the formed image.

[0120] Furthermore, specific control is performed when the average Q / M of the toner in the bottom toner layer of a multi-layer toner image is 0.8 times or less the average Q / M of the toner in the top toner layer, thereby improving the specific control's effect of preventing the scattering of toner in the bottom toner layer of a multi-layer toner image transferred onto a recording medium from affecting the formed image.

[0121] Furthermore, when the toner in the bottom toner layer of a multi-layer toner image is produced by a pulverization method and the toner in the upper toner layer is produced by a polymerization method, specific control is performed, thereby improving the effect of specific control in suppressing the influence of scattering of toner in the bottom toner layer of a multi-layer toner image transferred onto a recording medium on the formed image.

[0122] Furthermore, specific control is performed when the color of the toner in the toner layer other than the bottom layer of the multi-layer toner image is yellow, magenta, cyan, or black, and the toner in the bottom layer is a color other than yellow, magenta, cyan, and black, thereby improving the effect of specific control in preventing the scattering of toner in the bottom layer of the multi-layer toner image transferred onto the recording medium from affecting the formed image.

[0123] The present invention is not limited to the above-described embodiments.

[0124] For example, in an embodiment, the specific multi-layer toner image is formed by superimposing M (magenta), C (cyan), and W (white) toner layers. However, the specific multi-layer toner image may be formed by superimposing a color other than M (magenta) or C (cyan) on a W (white) toner layer. The specific multi-layer toner image may be formed by superimposing M (magenta) and / or C (cyan) and a color other than M (magenta) or C (cyan) on a W (white) toner layer.

[0125] Furthermore, the color of the bottom toner layer of the specific multi-layer toner image may be a special color other than W (white), such as gold or silver.

[0126] While embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are made for purposes of illustration and example only and are not intended to be limiting, and the scope of the present invention should be construed by the language of the appended claims. [Explanation of symbols]

[0127] 41Y, 41M, 41C, 41K imaging units, 414 photosensitive drum, 415 Primary transfer roller, 42 intermediate transfer belt, 43 Secondary transfer roller, 50 fixing section, 51a fuser roller, 52 pressure roller, 71 conveying route, 72 conveying roller, 80 ADU transport route, 100 Image forming device, 110 control section, 120 storage section, 130 Communications Department, 140 Operation display section, 150 image reading unit, 160 Image control unit, 170 Image forming unit, 500 toner layers, 501 toner, 510 toner image, 900 film.

Claims

1. An image forming apparatus in which toner layers are superimposed on an intermediate transfer body to form a toner image, and the formed toner image is transferred onto a recording medium, An image forming apparatus having a control unit that performs specific control to reduce the volume of the toner layer of the same color as the monochromatic toner layer, which is the bottom layer of the multi-layer toner image transferred onto the recording medium when forming a multi-layer toner image by overlaying toner layers of multiple colors in the same pattern as the monochromatic toner layer, compared to the volume of the monochromatic toner image transferred onto the recording medium when forming a monochromatic toner image.

2. an image signal generating unit that generates an image signal based on print data; a toner image forming unit that forms the toner image based on the image signal, 2. The image forming apparatus according to claim 1, wherein the control unit performs the specific control by causing the image signal generating unit to generate the image signal in which the area of ​​the bottom toner layer of the multi-layer toner image to be transferred onto the recording medium is reduced by a predetermined number of pixels from the area of ​​the top toner layer.

3. A photoreceptor; a charging unit that uniformly charges the photosensitive member; a writing unit that forms an electrostatic latent image on the photosensitive member by using a laser; a developing unit that develops the electrostatic latent image formed on the photosensitive member with toner, 2. The image forming apparatus according to claim 1, wherein the control unit performs the specific control by reducing the amount of light of the laser that forms the electrostatic latent image for forming the bottom toner layer of the multi-layer toner image to be transferred onto the recording medium.

4. A photoreceptor; a charging unit that uniformly charges the photosensitive member; a writing unit that forms an electrostatic latent image on the photosensitive member by using a laser; a developing unit that develops the electrostatic latent image formed on the photosensitive member with toner, 2. The image forming apparatus according to claim 1, wherein the control unit performs the specific control by reducing a development voltage applied by the development unit when developing the bottom toner layer of the multi-layer toner image transferred onto the recording medium.

5. a primary transfer section that contacts a photosensitive member via the intermediate transfer member and transfers the toner layer on the photosensitive member onto the intermediate transfer member; 2. The image forming apparatus according to claim 1, wherein the control unit performs the specific control by changing the primary transfer bias of the primary transfer unit when transferring the bottom toner layer of the multi-layer toner image to be transferred onto the recording medium onto the intermediate transfer body.

6. a secondary transfer section that contacts the intermediate transfer body with the recording medium interposed therebetween and transfers the toner image on the intermediate transfer body onto the recording medium; 2. The image forming apparatus according to claim 1, wherein the control unit performs the specific control by changing a secondary transfer bias of the secondary transfer unit when forming the multi-layer toner image on the recording medium.

7. The image forming apparatus according to claim 1 , wherein the control unit changes the amount of reduction in the volume of the bottom toner layer of the multi-layer toner image in the specific control, depending on the acquired type of the recording medium.

8. 2. The image forming apparatus according to claim 1, wherein the particle size of the toner in the lowermost toner layer of the multi-layer toner image is 1 [mu]m or more larger than the particle size of the toner in the upper toner layer.

9. 2. The image forming apparatus according to claim 1, wherein the circularity of the toner in the lowermost toner layer of the multi-layer toner image is smaller than the circularity of the toner in the upper toner layer by 2% or more.

10. 2. The image forming apparatus according to claim 1, wherein the specific gravity of the toner in the lowermost toner layer of the multi-layer toner image is 1.3 times or more greater than the specific gravity of the toner in the upper toner layer.

11. 2. The image forming apparatus according to claim 1, wherein the average Q / M of the toner in the lowermost toner layer of the multi-layer toner image is 0.8 times or less the average Q / M of the toner in the upper toner layer.

12. 2. The image forming apparatus according to claim 1, wherein the toner in the lowermost toner layer of said multi-layer toner image is produced by a pulverization method, and the toner in the upper toner layer is produced by a polymerization method.

13. 2. The image forming apparatus according to claim 1, wherein the color of the toner in the toner layer other than the bottom layer of the multi-layer toner image is yellow, magenta, cyan, or black, and the color of the toner in the bottom toner layer is a color other than yellow, magenta, cyan, and black.

14. 1. A control method for an image forming apparatus that forms a toner image by superimposing toner layers on an intermediate transfer body and transfers the formed toner image onto a recording medium, comprising: A control method comprising a step of reducing the volume of the bottommost toner layer of the same color as the monochromatic toner layer of a multi-layer toner image transferred onto a recording medium when forming a multi-layer toner image by overlaying toner layers of multiple colors having the same pattern as the monochromatic toner layer, compared to the volume of the monochromatic toner image transferred onto the recording medium when forming a monochromatic toner image.

15. A control program for an image forming apparatus that forms a toner image by superimposing toner layers on an intermediate transfer body and transfers the formed toner image onto a recording medium, comprising: A control program for causing a computer to execute a step of reducing the volume of the bottommost toner layer of the same color as the monochromatic toner layer of a multi-layer toner image transferred onto a recording medium when forming a multi-layer toner image by overlaying toner layers of multiple colors having the same pattern as the monochromatic toner layer, compared to the volume of the monochromatic toner image transferred onto the recording medium when forming a monochromatic toner image.

Images